Arboriculture

Standard Cyclopedia of Horticulture

Arboriculture. Arboriculture is the growing or cultivation of trees. It is distinct from sylviculture, which grows trees in forest plantations for the production of a timber-crop. Sylviculture is a part of forestry. What constitutes a tree is not easy to explain in a short and well-defined statement. A given species may assume a tree-like habit or remain shrubby, according to the climatic conditions, soil and other circumstances. Usually a tree is defined, under normal conditions, as a woody plant rising from the ground with a single stem and attaining a certain height, fixed by some at 20, by others at 15 feet, or even less. A more exact definition has been given by B. E. Fernow: "Trees are woody plants the seed of which has the inherent capacity of producing naturally within their native limits one main erect axis continuing to grow for a number of years more vigorously than the lateral axes and the lower branches dying off in time." Trees are the most prominent feature of the vegetable world and surpass all other organic beings in height, magnitude and longevity. The greatest height known has been reached by Sequoia sempervirens, which attains 340 feet Not very far less is Eucalyptus amygdalina, of which the highest tree actually measured is given as 325 feet; it is, therefore, the tallest of the hardwood trees. The sequoias, however, are of more majestic and gigantic appearance than the eucalyptus on account of their massive trunk (see Sequoia). Pseudotsuga taxifolia and Pinus Lambertiana occasionally attain 300 feet. A number of other conifers, chiefly American, grow to a height of 150 to 300 feet. Some deciduous trees, as Platanus occidentalis, several species of oak and Liriodendron Tulipifera exceed 150 feet in height. The jequitiba of southern Brazil (Couratari legalis, one of the Myrtaceae) is also a gigantic tree (see Bot. Gaz. 31, p. 352). The greatest diameter has been observed in Castanea vesca, of which a tree with a partly decayed trunk at the "foot of Mt. Etna in Sicily measures more than 60 feet in diameter. After this the greatest diameter observed is in Taxodium mucronatum, about 40 feet, and in Platanus orientalis about the same, in Sequoia gigantea 35 feet, in Taxodium distichum 30 feet, and somewhat less in Adansonia digitata. The age attributed to many of the tallest trees is based more or less on speculation, and opinions often differ widely. Dracaena Draco is believed to reach 6,000 years of age, Adansonia digitata 5,000, Taxodium mucronatum and Platanus orientalis 4,000, Cupressus sempervirens and Taxus baccata 3,000, Castanea sativa, Quercus pedunculata, Sequoia gigantea and Cedrus Libani more than 2,000 years. Although the trees are the most conspicuous features of the vegetable kingdom, they represent only a small percentage of it as regards the number of species. In the United States, where about 600 trees occur, they represent only about 3½ per cent of the whole phanerogamic flora, in Europe even less. As a rule; towards the tropics the number of tree-like species increases, towards the arctic regions it decreases. Remarkably rich in trees is the flora of Japan, where the proportion of trees to the whole phanerogamic flora is more than 10 per cent, which percentage surpasses by far that of any other country in the temperate regions. Trees belong to many different natural orders, but of the orders of monocotyledonous plants only a few contain trees and none of them is hardy North. None of the larger orders contains trees only, but there are some which consist exclusively of woody plants and include a large proportion of trees, as Pinaceae, Fagaceae, Salicaceae, Juglandaceae, Magnoliaceae, Sapindaceae, Elieagnaceae, Ulmaceae, Hamamelidaceae, Lauraceae, Anacardiaceae, Ebenaceae, Styracaceae and others. The uses of trees are manifold, and a country from which the forests have been destroyed becomes almost. uninhabitable and worthless to mankind. The forests furnish wood and timber, exercise beneficial influences on the climate, act as regulators of the waterflow, prevent erosion and also the removal of soil by the wind. Besides furnishing wood and timber, many trees yield other products of great economic importance, especially the numerous kinds bearing fruits. The esthetic value also of the tree must not be underrated, although it cannot be counted in money. The science of trees and shrubs is dendrology. The art of growing trees is arboriculture, while the rearing and maintaining of forests and the production of timber-crops is sylviculture. Arboriculture is sometimes used in a broader sense, like dendrology, to include also the growing of shrubs. Orchard culture is a branch of arboriculture or of horticulture, and deals with the cultivation of fruit trees; it is usually included under pomology, which comprises both the science and practice of fruit-growing. As ornamental subjects, trees are more permanent, easier of cultivation and cheaper in the long run than herbs. It is curious to note now little attention the average gardener who has the care of a park or garden gives to the most prominent feature of his domain. He usually knows fairly well the greenhouse plants and herbaceous perennials, which cost most in time and money, but the trees and shrubs he often disregards. This is apparently due to the fact that after being once planted, and often not by himself, the trees and shrubs do not need his perpetual care, and usually grow without his aid and interference. To the landscape gardener a thorough knowledge of trees is absolutely essential. He ought to know the ornamental properties of the trees, their rate and mode of growth, their peculiarities in regard to soil, situation and climate. As the trees are, after the surface of the ground, the most permanent element of the landscape, they ought to be planted with careful deliberation as to the intended artistic effect and their fitness to the soil and climatic conditions, for mistakes in planting of trees are afterwards not easily corrected and rarely without injury to the original artistic design. The available number of trees from which selection may be made is large. There are in American and European nurseries and gardens more than 600 species in cultivation that are hardy in the northern and middle states. About 250 of them are American, more than 200 from eastern Asia, about 100 from Europe and 70 from western and central Asia. About forty natural families are represented, of which the most important are the Pinaceae, Fagaceae, Salicaceae. Rosaceae, Leguminosae, Juguindaceae. Sapindaceae, Urticaceae, Magnoliáceae, and Oleaceae. The number of all the cultivated varieties and garden forms is, of course, considerably larger than that of the botanical species and may be estimated at about 3,000. Comparatively few horticultural varieties are found in American nurseries as compared with European, but this need not be regretted, as horticultural varieties are mostly merely curious or monstrous forms. In planting, one must rely chiefly on the types and use the horticultural varieties sparingly, for restfulness should be the prevailing character of the masses and groups of trees. The cultivation of trees From earliest times man's instinct has been to seek the protection of trees. In locating his home the first necessity has been the proximity of water; second, pasture for his flocks; third, the presence of trees; in warm countries it has been necessary to provide protection from the hot sun's rays, in cool countries for the sake of fuel and protection from the elements. As civilization has progressed and man has developed more elaborate abodes, he still desires the protection of trees to make his home more comfortable, to protect it from the winter wind, or the summer sun, or both. To meet the needs in different localities, as one or another protection may be more important, different kinds of trees are used. In the extreme North, the coniferous evergreens act as windbreaks twelve months in the year. In the south Atlantic and Gulf regions, the broad-leaved evergreens give shade the year through. In the intermediate country and overlapping both, the deciduous trees afford much summer protection and a little winter protection. The chief aesthetic value of trees is due to the suggestion of comfort that they give. In winter, a house snuggling against a group of evergreens may be attractive, and yet, if lacking a well- placed shade tree, may in summer appear glaring or otherwise uninviting. These feelings are the same with regard to native woodlands or man-made clumps more remote from dwellings. The different kinds of forest attract because of suggestions of comparative comfort and of pleasures. To those who have lived in the heart of a large city all their lives, such scenes are likely to be unattractive because of lack of suggestiveness. Some of the interesting and varied forms of trees are displayed in Figs. 312 to 359. In planting trees for ornament, these elements of protection suggest two uses, that of windbreaks and that of producing shade at appropriate places. In addition are the partial hiding of buildings from important viewpoints, enhancing the beauties of the building or permitting only the most desirable features to be seen, covering the outlines of ugly buildings, or completely hiding objectionable objects, either nearby or distant; forming frames for distant views or nearby objects; making knolls and hills look higher by groves on their tops, or valleys look deeper because of wooded sides; making irregular sky lines either by accentuating existing conditions by planting tall trees on the high places and low trees in the low places, or in level countries making a similar sky line by tall and short trees; or forming irregular and natural appearing boundaries to lawns or meadows. To accomplish any of these results, some trees are inherently better suited than others; climate and soil, however, may make their use impracticable or impossible. Coniferous evergreens make the ideal windbreak and screen, but they are satisfactory only in the northeastern section of the country and on the Pacific Coast, the hot sun of the South, the dry winds of the central plains and the smoke of cities making most species impossible in those regions. The broad-leaved evergreens are next in importance, but they are adapted only to the south Atlantic and Gulf seaboards, and the Pacific Coast north of San Francisco. For adaptabilities see special lists, for no other sweeping generalizations of adaptabilities can be made except that the use of bronze, yellow or variegated-leaved trees, and trees of unusual drooping habit or of other striking form, should be limited to special times and places. A tree to be satisfactory for ornamental planting must suit the climate and maintain the appearance of healthy growth on the soil where planted, must be hardy, and must be free from serious insect and fungus attacks. The location of trees is a detail of the design of the place. This is intimated in the preceding paragraphs and more fully discussed under Landscape Gardening, but a few cautions may be in order. Do not so surround the house with trees that they exclude all the sunshine. Except in the extreme South, use deciduous trees next the house so as to have full benefit of the winter sun. Plant the evergreens at a little distance. For specimen trees of the larger kinds, plant 50 to 100 feet apart, depending on the kind. For thickets and quick masses of foliage, the same kinds may be planted 15 feet apart. Theoretically, planting more trees than are ultimately necessary and then thinning is excellent. Practically, it is dangerous as there is not one chance in ten that it will be done in time. Plant irregularly both as to distance and direction unless the design is strictly formal, in which case plant with mathematical precision. When and how to plant There is great difference of opinion as to the best time to plant. In climates with the temperatures of Boston, Rochester, Chicago and farther north, spring planting is probably best for most plants. Fall planting is increasingly more satisfactory as one goes south. On the western plains where strong, dry winter winds prevail and the soil is either so dry or freezes so hard that a newly planted tree cannot replenish the moisture taken out by the winds, spring planting is most successful. The character of soil may also have its influence. Magnolias and tulip trees should always be planted in spring. Coniferous evergreens should be planted either when growth has started is spring or, when vigorous, in late summer or early fall. Other evergreens should be planted when entering the period of most active growth so as to be able to form roots quickly to support the foliage that is always present. The period of generous moisture in air and soil is most favorable for the planting of evergreens. In adverse seasons, these conditions may be in a measure produced by liberal watering of the soil and frequent spraying of the tops. Deciduous trees should be planted when dormant, in order that roots may become well formed before there is foliage to support. Large holes should be prepared for planting, at least 2 feet larger in diameter than the spread of the roots of the lifted tree, and 2 feet deep. If the soil is good, no further special preparation is necessary beyond a liberal mixture of well-rotted manure or raw bone-meal with the soil to be replaced in the hole, and supplying new top- soil to replace any subsoil excavated in digging the hole. In poor ground, a hole at least 6 feet across and 2 feet deep should be dug for a tree up to 8 feet high, and for larger trees proportionately larger holes to give them good ground for beginning growth. It is becoming common to dynamite holes for trees. Just how far this is desirable is yet problematical. In tough subsoils, it appears to be eminently successful. It seems reasonable to suppose that in most subsoils such a loosening would be permanently beneficial. Careful observers have noticed that trees usually thrive better on filled ground than on nearby soil where the land has been undisturbed, even though the fill appears poor in comparison. This does not have reference to city ash and garbage dumps. The ashes are too inert to support tree growth, the dump is frequently poisonous. In large plantings, the watering of deciduous trees and the staking of trees under 10 feet is usually omitted in the moist regions in which strong winds do not prevail, the replacing of any losses being considered more economical than this additional expense. Larger trees need special attention. The size of trees to choose varies with the kind, the purpose, and the need for quick results. Trees may be successfully transplanted from one- or two-year-old seedlings to those 12 or 16 inches through and 40 feet high, success depending largely on the skill of the planter. Usually trees 6 to 12 feet high are best for deciduous trees, 3 to 6 for coniferous. Some species succeed better with small sizes, as tulip tree, magnolias and hollies. Nursery-grown trees that have been frequently transplanted are best, as they transplant with less loss because they have an abundance of fibrous roots. Collected stock of some kinds is satisfactory for mass-planting but the loss will run from 50 to 90 per cent, depending on kind and condition. Trees that are very small are not desirable to use, as they grow no better than larger nursery-grown trees and the cost of cultivation is more when planted permanently than when in the nursery row. Trees above the sizes mentioned are expensive to handle and the loss is likely to be greater. When immediate results are important, these are worth using with a mixture of smaller trees to take their place in case they should be short-lived. Pruning and tree-doctoring At planting, all broken limbs should be removed as well as any crossing through the head or below it. If the top is still crowded, some limbs may be removed by cutting them off at the nearest fork. Heading-in or shortening the limbs is undesirable with most species. The magnolias and tulip tree are exceptions to this; they need severe shortening-in when transplanted. All roots should have the broken ends cut off with a smooth, clean cut, as this freshly cut surface seems to facilitate the formation of new rootlets or at least to prevent decay. If a newly planted tree is very slow in starting, it is sometimes induced to grow by a severe pruning. Desirable varieties of shade trees seldom need any heading back. An annual inspection with slight pruning to shape the tree and remove surplus branches is all that will be required. A tree should be grown into shape, not pruned into shape, and should be allowed to develop its own characteristics. Evergreen trees, with the exception of the evergreen oaks and Magnolia grandiflora, should be trained so that their foliage rises directly from the turf. As it grows old, the white pine is likely to bare its trunk in spite of other training. Spruces and other coniferous trees are ruined if pruned to show the trunk. Figs. 318, 319. Many deciduous trees are also most attractive when their lower limbs rest on the ground, as beeches, the Norway maples, hornbeams and many more, any tree in fact whose natural habit will permit such a form. Old trees, owing to neglect, or more often, improper pruning, frequently need the saw. Protruding stubs should never be left, whether the tree is large or small. The cut should always be made close to the remaining limb and parallel with it. It will not require over two years for the callus to show all around a properly made cut. If it does not show then, the work should be done over again. All dead wood should be kept out. Crossing limbs, even if large, should be removed. A tree should not be dehorned, i.e., cut back to stubs 3 or 4 inches or more in diameter, except as a last resort for a failing tree. Pruning is employed for two distinct ends: to train and shape a young tree as it grows; and to re-form or adapt a tree of some maturity, especially if somewhat decrepit. The so-called "tree-doctoring" or "tree- surgery" is applied especially to the latter phase. A tree that has become weakened by transplanting, or from lack of proper nutrition, from lack of proper fertility, or scarcity of water, or from other undetermined causes, may often be forced into active vigorous growth by a severe cutting-back. It may even be allowable, in such cases, to pole or dehorn a tree; that is to remove most of the small limbs, cutting the large ones so close to the tree as to leave stubs as large as one's wrist or arm or even larger. It never happens that several trees in a row need such treatment unless their feeding-ground has been greatly depleted. Trees that have been badly pruned, broken by wind, storms or otherwise bruised or mistreated, frequently have badly decayed spots in their trunks and limbs. It has become the custom to "doctor" such trees,— that is, thoroughly to clean out rotten wood, treat the exposed surface with a solution of corrosive sublimate or sulfate of copper to kill any fungous growth that may be present, with bisulfide of carbon or other insecticide for insects, and then coat the surface with tar as a preservative. After this the cavity is carefully filled with concrete of the strength commonly used in construction work. It is absolutely essential to success that the joint between the wood and cement be water-tight. The surface should also be given a smooth finish of the general outline that the tree would assume had it grown normally. The finished surface should coincide with the inner edge of the cambium layer so that the growth of the tree will proceed over the cement just as it would over a properly cut stub. Zinc caps are frequently used both to cover cement fillings to keep out the water and to cover large cuts when the wood is solid but when it will take several years to heal on account of the size of the wound. Cavities must be absolutely clean, thoroughly disinfected, and the filling positively water-tight or decay will begin behind the filling and the tree will be destroyed while every confidence is being felt that it is safe. The cement work is frequently reinforced with rods of iron. Its principal value is to hold the cement from cracking. The only value of such cement work is as a preventive of decay where there are cavities. When properly done, it gives a smooth surface over which the growth may proceed. The supporting value of the cement to the tree is slight. With many hardwood trees in important locations such treatment is warranted, but at the present time many trees are thus treated that should be cut down, while many others are left that should have attention. The first requisite to warrant the treatment of a large cavity is a good type of tree in an important location, for example a large tree protecting the home from the mid-afternoon sun, or a bad individual in an avenue of otherwise good specimens. In large plantations, treatment of a preventive nature is of course warranted, but the filling of large cavities is not worth the cost except to those to whom money is little object. It is better to start new trees than to spend fifty dollars on patching up an old one. One must exercise careful judgment in selecting old trees for treatment, to make sure that the tree is worth it. Trees worth doing work on are the oaks, sugar, swamp and Norway maples, hickory, ash, elm and the slow-growing native trees. Those not worth treating in this way are the poplars, willows, silver- and ash-leaved maple and sycamore or plane tree. A street tree with a large cavity would better not be doctored unless it is of special value and of a kind likely to last a long time. Badly branched trees often show a tendency to split in the crotches. It is well to attend these trees before they begin to split and either chain or bolt the offending limbs together. They may be chained by putting lag- screws in the limbs, drawing the limbs together and dropping a link of the chain over the turned up end of the screw. Rods and turn-buckles may be used in the same way, the bolts for the rods being put through the limbs, not around them. Because bolts have to be placed closer to the weak point than the other remedies, they are not so effective but are often useful. If a tree splits, there is danger of decay. The splitting should be anticipated and prevented whenever possible. The best time for pruning is not a question of invariable rule. The period of most active growth, in most places June, is usually regarded as the best time. The period of starting into leaf is probably the worst time, although the maples are about the only good shade trees that seem much affected by pruning at this season. Large cuts or wounds should be immediately painted with a good grade of paint or with tar, care being taken to cover the exposed wood but not to allow the paint to come into contact with the cambium layer, or growing part of the bark. Root injuries should be as zealously guarded against as injuries to the top. If a large part of the roots must be removed, the top should be correspondingly thinned. Changes of grade are a great source of damage to shade- trees, even when the roots are not actually touched. The filling of 2 or 3 feet of soil over the roots of a tiee is, for most varieties, as sure death to the roots as cutting them off close to the trunk. This filling prevents the aeration of the soil and smothers the soil life on which healthy root-action seems to depend. This may be prevented by a good layer of loose stones, open at intervals to the air, placed over the surface before filling, or, in some cases, by the use of agricultural tile drains on the old surface at close intervals and so arranged as to facilitate a free circulation of fresh air through the tiles. Street trees In the development of towns and cities, the need of trees as a protection against wind has been reduced to a minimum since the closely built houses protect one another. This close building, however, has brought about another untoward condition that needs ameliorating; this is the replacing of the vast extent of green, common to the open country, by a motley array of discordant colors. Many of these colors have been demonstrated experimentally and practically to have exciting and debilitating effects on the physical condition of persons. Part of the great utility of parks is to afford urban residents relief from this color excitement. As far as possible, the soothing green needs to be taken into the city streets to rest the tired nerves through the effect on the eye. Also, the shade helps to reduce the temperature by absorbing the sun's rays; the large amounts of water the tree transpires also helps to cool the air. These beneficial effects make it worth while to expend effort and money to secure well-shaded streets. Figs. 323, 324. The conditions in' urban communities are adverse to tree growth. Streets are narrow and the trees crowded; roadway and sidewalk are paved with impervious materials preventing both water and air getting into the soil, and effectually keeping in sewer-gas and illuminating-gas that may be discharged into it from below. The air is dust-laden from constant traffic, and, what is far worse, contaminated by soot and poisonous compounds from numberless badly-fired chimneys. As though this were not enough, there are the self-styled tree-trimmers, knowing nothing of the work, then the linemen cutting ruthlessly, caring nothing for the tree, and with an occasional gnawing horse adding its demolition. And the sewer-layer, pipe- or conduit-layer and finally the curb-setter do their worst. After all of these, come the insects and diseases that affect trees everywhere and which here find an easy prey because of the fewer birds in city streets and the weakened condition of the trees. The first essential to successful street tree-planting is competent municipal control of all such work. The street trees should be under the care of an unpaid commission of three or five men, one named every two years by a local court, or by the mayor, for a term of six or ten years, and confirmed by the legislative body. Such commissioners usually need to be trained, and therefore they should have considerable experience in their work before coming into full responsibility. The restrictions on the appointment of the executive officer should be stringent, so that only thoroughly trained and experienced men could be employed. The expert should have the full confidence of the commission and be the leader in the work. To fill such a position, a man should have thorough knowledge of trees and the soils and conditions under which they grow, their characteristics, aesthetic values and habits of growth under city conditions, the methods of aiding trees to withstand these conditions, and a knowledge of the insects and diseases to which the different species are liable and the methods of combating them. The work is neither forestry nor pomology, as it has nothing whatever to do with the products of tree growth or the growing of trees for their fruits. Powers vital to the success of this commission are the right to plant suitable kinds of trees in a proper way. and to collect benefits for work so done; to control absolutely all pruning, removal and care of trees; and the right to invade private grounds for the control of insects and diseases. Of course, sufficient funds must be available to support the work. Many city streets are too narrow from building-line to building-line for satisfactory planting. There is absolutely no excuse for this in the newer sections. There should be at least 100 feet from building-line to building-line on any street and on principal streets considerably more. Forty feet may be all that is needed for roadway and sidewalks, at present. The abutting dwellers need the air-space provided by the remaining area which is legitimately used as front lawns. This will leave ample space for trees. If the city grows and more space is needed for traffic, it can be secured with no sacrifice to buildings and the dwellers in the interval have had better living conditions. It is this arrangement that makes Washington such a beautiful city, and the lack of it on Fifth Avenue that is costing New York City so much money to widen that thoroughfare. In the older parts of cities, species must be chosen that are appropriate to the width of the street. Most kinds should be planted not closer than 40 feet apart and such varieties as oaks, elms and sycamores would be better at 50 feet. Most planters use 35 and 40 feet because of the public demand for quick shade, and at the greater distances the trees look far apart when first planted. Theoretically, the planting double the number of trees needed at maturity or the placing of fillers of a quick- growing inferior type, is desirable; but practically it is dangerous, as there are not many cases in which public opinion will tolerate the thinning at the proper time. In city work an excavation 2 feet deep, with the removal of at least 2 cubic yards of dirt, should be made for each tree. This should be filled with good top-soil mixed with well-decomposed manure. Of most varieties, trees 10 to 12 feet high and 1½ to 2 inches caliper should be used. These should be nursery-grown. They should have been frequently transplanted and have a well- developed head, 6 to 8 feet from the ground. The roots should be abundant and fibrous. In planting, the roots should be spread out and separated to their full length, the ground worked all in amongst them, and then thoroughly finned by tramping. Before the hole is completely filled, the tree should be well watered and the remainder of the soil put in loosely. A strong stake 8 feet long should be placed beside the tree when planted. At least 30 inches of this should be in the ground. The tree may be attached to the stake by a piece of old garden hose attached to each side of the stake and put around the tree in such a manner as to make a cross between the stake and the tree. All young trees should be protected by boxes or guards. Many forms are used. Any of them are good if the box reaches from the ground to a height of 5 feet and will prevent horses biting the trunks and boys swinging on the guard. Notes on ornamental trees Acer Negundo (box elder). Too short-lived, brittle and subject to insect attack. Its use may be warranted in semi-arid and very cold regions. Acer platanoides (Norway maple). Moderate grower, healthy, but too dense for close city streets. Acer rubrum (swamp maple, scarlet maple). A good- sized tree, good grower, fine foliage, especially brilliant in autumn. Also a bright red in spring due to blossoms and young leaves. Not suited to the interior of large cities. Acer saccharinum (silver maple, soft maple). Rapid grower, but too brittle and short-lived, and the shallow roots prevent the growth of grass under it and also destroy sidewalks. Acer saccharum (sugar maple). Does not thrive on heavy clay soils or under severe city conditions but most excellent where it does grow. Moderate grower, doing best north of the 40th parallel. Ailanihus altissima (ailanthus, tree of heaven). A large, handsome tree, the staminate and pistillate flowers appearing on different trees, the latter very ill- smelling. A most useful tree in the center of large cities. The staminate form only should be planted. Celtis mississippiensis (southern hackberry). An excellent tree in those regions in which the "witches- broom" does not attack it. One of the promising trees to withstand the hot winds of the plains as far north as Denver. A large tree and good grower. Celtis occidentalis (hackberry). A good tree where the disease known as "witches' broom does not attack it. It is for regions north of the 36th parallel what the foregoing species is for the region south of it. Fraxinus americana (ash, white ash). A good tree for suburban conditions. Moderate grower, attaining large size. Ginkgo biloba (ginkgo, maidenhair tree). An excellent tree of peculiar pyramidal form when young. Moderate grower, attains good size and is free from insect and fungus attacks. Gleditsia triacanthos (honey locust). A large, quick- growing, handsome tree. Except for its thorns, this tree would probably be a most desirable tree for the semi- arid regions of the West. There is a thornless form that may sometimes be obtained, which is good. Giant specimens 225 ft. high, grown in the deep, moist soil of the Yosemite Valley. Liquidambar Styraciflua (sweet gum). A handsome and valuable native tree but little used. Moderate grower, good size, handsome fall coloring. A little hard to transplant, especially in large sizes. Does not succeed well under extreme city conditions, and is not adapted to the extreme northern sections. Liriodendron Tulip/if era (tulip tree). Miscalled yellow poplar, and tulip poplar. A handsome, large, quick-growing tree, little used, but valuable except for extreme city conditions and much of the country north of the 40th parallel. A little hard to transplant, especially in large sizes, and should be moved only in spring. Magnolia grandiflora, A broad-leaved evergreen of large size, adapted to the extreme South. A good lawn tree as far north as Washington. Magnolia acuminata (cucumber tree). A handsome tree of moderate size, good for suburban conditions south of Washington and St. Louis. Magnolia tripetala (umbrella tree). A handsome tree of moderate size, good for suburban conditions south of Washington, and St. Louis. Melia Azedarach (umbrella tree). A small, attractive tree, good for temporary effects from North Carolina south and west. Nyssa sylvatica (sour gum, tupelo). A large, handsome tree, adapted to suburban conditions. Brilliant fall foliage and winter berries. Platanus occidentalis (sycamore, buttonwood). A large tree, rapid-growing, open-topped, and almost scraggly in its growth. Considered an untidy tree by some on account of its seed-balls and the bark which is shed in large flakes. The white trunk, after the bark is shed, is unusual and attractive. In some regions it is subject to a blight just after the leaves start in spring. A good tree for severe city conditions. Platanus orientalis (plane tree, oriental plane). A more compact grower than the foregoing and a little better suited to street purposes, but not quite so rugged and imposing as the foregoing. An excellent street tree. Populus deltoides, including var. caroliniana (cottonwood and Carolina poplar). These two trees are much used for street planting in many places but are entirely unsuited for the purpose. Although the growth of a severely pruned tree is large in any one year, it is the custom to remove a half of this each year so that the net gain in growth is no more than an average tree. Even with this pruning it is liable to be broken by a moderate wind storm, and without the pruning it is even more liable to be broken. Their roots are as bad as willow roots about finding and clogging sewers. Wide-awake cities prohibit the planting of these trees. Populus nigra var. italica (Lombardy poplar). A tall, short-lived, fastigiate tree, suitable for narrow streets in the heart of a large city. Quercus alba (white oak). A most picturesque tree, attaining the largest size. The gem of American trees, and not so slow-growing as usually considered. Dead leaves hang on most of the winter. Figs. 313, 322. Quercus bicolor (swamp white oak). A large, handsome oak of moderately rapid growth, suited to moist situations. It seems to succeed under city conditions. A desirable shade tree, almost as handsome as the white oak and a little faster grower. Quercus coccínea (scarlet oak). Comparable to the red oak but not quite so sturdy and vigorous under all conditions, but with a little more brilliant autumn coloring and leaves more finely cut. Quercus laurifolia (laurel oak, water oak). The standard street tree for the South. A large, handsome, deciduous tree, not so desirable as the live oak, but of more rapid growth. Quercus Michauxii (cow oak). A good oak for thin gravelly lands. Not so desirable as the other oaks on good ground and not adapted to the extreme northern sections. Quercus macrocarpa (mossy-cup oak). A handsome and satisfactory tree, not so large as some of the others. One of the most promising for the plains. Quercus nigra (possum oak, water oak). Another good oak south of Norfolk. A little more upright in growth than Q. laurifolia, but not quite so desirable except possibly in its more northern limits. Quercus palustris (pin oak). A quick-growing, good- sized tree, with pendulous branches when old. Handsome cut leaves, brilliant in autumn. One of the best. Its pendulous branches may sometimes be a rather serious objection. Dead leaves hang on well into the winter. Fig. 323. Quercus phellos (willow oak). A large, handsome tree, moderately fast-growing, satisfactory south of Washington in regions in which it is not attacked by a growth resembling "witches' broom" of the celtis. Quercus rubra (red oak). Almost the best street tree. Large, symmetrical, rapid in growth, fine autumn foliage, head not too dense. It is exceeded only by the elm in rapidity of growth among the trees suited for street planting and not by that in the southern half of the country. Quercus virginiana (live oak). A large evergreen. The best street tree for the South, but slower in growth than Q. laurifolia. Sterculia platanifolia (varnish tree). A small tree of reasonably rapid growth bearing bright yellow flowers. It has a tropical suggestion. Good only for the South and its principal value is in its possibilities for the Southwest, especially semi-arid Texas. Tilia americana (basswood, American linden). A large, handsome, quick-growing tree. Young trees are sometimes affected by a disease at the base of the trunk, but the tree is well worth growing except in regions in which the difficulty is known to be present. Ulmus americana (elm, white elm). The shade tree of New England and deservedly ranked first there. It loses its preeminence as one goes from New England, but a large, quick-growing tree worth using except in the extreme South. Drops its foliage too early to be the ideal shade tree in the middle states and southward. It is subject to the attacks of the elm-leaf beetle in regions in which that has been introduced. The conifers in particular The cone-bearing trees (Pinaceae and allies) are decidedly the most important order of forest trees in the economy of civilized man. They have furnished the bulk of the material of which our civilization is built. The remarkable combination of strength and stiffness with the smallest weight compatible, and the abundance and gregariousness of their occurrence, give them this important position. From the standpoint of the horticulturist, the conifers also take a prominent place among the materials for landscape gardening effects, and, in the more practical use, as windbreaks. Their evergreen habit — for all except the larch and ginkgo tribes are evergreen — and their conical form, especially in earlier periods of life, with a branch system persisting to the base for a long time, are the elements that make them , desirable. To these graces may be added the peculiar form and striking coloring of their foliage, which, in combination with deciduous trees or in clumps by themselves, or in single specimens, offer striking effects. There are two types of natural or native beauty in the conifers — the symmetrical and verdurous beauty of the young specimen (Figs. 318, 319), and the picturesque and rugged beauty of the old and timeworn tree (Figs. 315-317). Aside from these, there are also odd, grotesque and formal cultivated varieties, as typified in the weeping spruce (Fig. 320), the columnar junipers, and the various dwarf pines and spruces. The majority of the species belonging to this group, as well as their greatest numerical development, is found in the temperate zones, only a few belonging to subtropical or tropical countries, among which are the araucarias, from South America; the dammara, dacrydium, and phyllocladus, from Australia, and neighborhood. Kinds and adaptations The order Coniferae comprises nearly 40 genera, and about 300 species. Our own native flora, with 15 genera and not less than 100 species and subspecies, is among the richest, the bulk of these being found on the Pacific coast. The Altantic side offers 28 species, representing the genus Pinus with 12 species out of 39; 1 Larix out of 3; 3 Piceas out of 7; 2 Tsugas out of 5; 2 Abies out of 12; 1 Taxodium; 1 Thuja out of 2; 1 Chamaecyparis out of 3; 3 Juniperus out of 11 ; 1 Turnion (Torreya) out of 2; 1 arborescent Taxus out of 2: being without representatives of the genus Pseudotsuga. Sequoia, Libocedrus, and Cupressus. There are to be added a large number (not less than 400) of nurserymen's varieties, some of which have been enumerated in Bulletin 17 of the Division of Forestry, United States Department of Agriculture. There are also a number of exotic conifers that promise satisfactory results if used in suitable localities, climate and soil. The Norway spruce (Picea excelsa, Fig. 356) recommends itself by its elegant gothic form, often with pendulous branchlets, its very rapid growth, and its wide adaptation to soils and climates, together with its ease of propagation and cheapness. It excels most of the American spruces in form and rapidity of growth. Like all conifers, after the twenty-filth to fortieth year it must pass through a period of change in form, during which it loses, for a time, its shapeliness. The Scotch pine (Pinus sylvestris) has nothing to recommend it which may not be found in native species, except, perhaps, adaptation to the dry climate of the West, and cheapness. The Austrian pine, on the other hand, is an acquisition by its stout growth in its youth, although the red pine (Pinus resinosa) would probably do as well; so far, its small cones and seed have made the latter expensive. The European larch outgrows the native northern one easily, but Larix occidentalis, from the interior basin, will probably do as well or better. There is no particular commendation for the European fir, but the Nordmann fir, from the Caucasus, is a most decided aquisition, by its beauty and adaptation; so is the most graceful of all spruces, Picea orientalis, while the Spanish Abies Pinsapo (Fig. 318) will always attract attention by its peculiar shape and foliage. Of other ornamental forms that are without repretatives in the United States and hence fill vacancies, may be mentioned as capable of adaptation and more or less in use, from South America, the araucarias; from Africa and eastern Asia, Cedrus Deodara, libani, atlantica, Abies Apollinis and cilicica; from Korea, the promising, more densely foliaged white pine, P. koraiensis; from China, Cunninghamia, Biota, Glyptostrobus, Cephalotaxus, Podocarpus, Pseudolarix, and, above all, that interesting remnant of former ages, the maidenhair-tree, Gingko biloba, which will maintain itself anywhere along the Atlantic coast if propagated from seed of the proper localities. Japan has furnished a number of additions, especially retinosporas, torreyas, taxus, various pinus, piceas and tsugas, with the peculiar Sciadopilys verticillata, the umbrella pine, and, the most acceptable of all, the graceful Cryptomeria japonica. As with all introductions from one country to another, nay, from one climatic region to another, caution is advised, so it may be laid down as a rule, that exotics should be used with great discretion, and, until their adaptation is amply demonstrated, only in a subordinate way. If it is in general true that perennial plants can be transplanted with permanent success only into similar climatic conditions, it must be especially true with the conifers, which do not lose their foliage, and hence must be able to bear summer as well as winter conditions. The long-leaf pine of the South, most striking of our pines, may, therefore, not be transplanted far beyond its northern limit, and, if one desires to utilize any of the Pacific coast species in the East, one will have to secure them at least from the highest and driest altitudes and exposures, or if, as in the case of some species, like the Douglas fir and Engelmann spruce, their field of distribution covers the dry slopes of the Rocky Mountains as well as the moist slopes of the coast ranges, one may be successful if one chooses the plant material from these drier slopes. Of the many native species, a number that are not of any particular value may be discarded, although the distinction could be more readily accomplished from the economic point of view than from the standpoint of the horticulturist and landscape gardener, for almost every one has a distinctive feature of either form or adaptation to soil or other interest. For each climatic region the choice must be different; hence it would be impossible to give, in the brief space of an article, intelligent advice as to best selections. In general, besides climatic limitations, the following considerations may serve in the choice of native species: The pines, as a rule, are not to be placed on compact clay soil, and on account of their taproot, not on shallow soils, on which they soon become spindly; they thrive best on loose, sandy soils, and can endure dry soils, the white pine adapting itself perhaps best to the clay soils without detriment to its development. On wet soils pines are, as a rule, decidedly out of place, although the red pine (P. resinosa), of the North, and the loblolly (P. Taeda), and some other southern species are capable of supporting such conditions. For such situations here, however, the cedar tribe furnishes better material,—the chamaecyparis, thuyas and taxodium. These trees of the bog and swamp are, however,—it should not be overlooked,—capable of thriving even better on drier soils. They are merely indifferent to moisture conditions at the foot. The shallow-rooted spruces are trees of the higher mountain ranges, and are, therefore, more adapted to moist and cool situations, although some of them, the Norway spruce, the blue spruce of Colorado and the northern white spruce will—the former, at least, during its juvenile period—endure more droughty situations. The firs, too, are rather more species of northern climates and high altitudes, the red fir, so-called (Pseudotsuga taxifolia), which is not a fir proper, being, perhaps, best capable of supporting drier and hotter situations. The most ornamental, and, in many respects, most serviceable of the firs, Abies Nordmanniana, from the Caucasus, develops its magnificent dense and dark green foliage in the warm but moist climate of Washington, while our most ornamental Abies concolor from Colorado will thrive even in the drier atmospheres of the middle states. The fine firs of the Pacific coast will probably not thrive anywhere in our drier and hotter eastern climates for any length of time, unless placed in cool and shady situations. The Douglas fir (Pseudolsuga taxifolia) is, perhaps, most readily acclimated if seed is secured from the dry slopes of Colorado. The Lawson cypress (Chamaecyparis Lawsoniana), with its graceful pendulous branches and foliage, and the pyramidal Libocedrus decurrens are unquestionably desirable additions to our ornamental stock, while the sequoias, especially S. gigantea, the big tree, seems not to be able to support persistently our eastern climate. One important feature which enters into consideration when grouping conifers is the relative endurance of shade or tolerance which the species exhibit, thereby indicating their use in" various positions. The yews and firs are the most tolerant of shade, together with the hemlocks; next may be placed the spruces, arborvitae (Thuya), and junipers, while the pines are mostly intolerant of shade, excepting the white pine, which is the most shade-enduring of the pines; the larch and the bald cypress are the most light-needing of all, and will perish soon if placed under the shade of any other trees. All species, to be sure, are capable of more shade-endurance when young and on deep, moist soil. Their relative shade-endurance under the same conditions remains, however, the same, and may be studied in the forest by observing the density of the individual crowns, the capacity of maintaining a thrifty foliage under the shade of different species, and especially of young plants to persist in such shade. Propagation Most conifers ripen their fruit in the fall, September to November, and are best gathered soon after or before ripening. The pines require two years (some three years) to mature their cones. White pines ripen fruit in the first two weeks of September, and the cones opening shed the seeds at once, the empty cones remaining on the branches. The cones of the firs fall apart upon ripening, hence must be gathered before being quite ripe. Spruces and hemlocks shed seeds from time to time, opening and closing their cones according to the weather through the winter into spring. Some pines, like Pinus pungens and P. serotina, keep their cones closed for years, and artificial heat must be employed to make them open and give up their seed. In gathering seeds for the trade, such artificial heat is frequently applied with pines in specially constructed seed-roasters; such seed should be carefully inspected, as it sometimes suffers from improper use of the heat. The proportion of germinating seeds, and the vitality, i.e., the ability of retaining germinative power, varies greatly not only with the seasons in the same species, but from species to species. The lowest germination percentage and vitality is found in firs and larch, which show rarely more than 50 per cent of good seed, and soon lose their vitality, while spruce and pine, when entirely fresh, may show as much as 95 to 100 per cent germination, and retain vitality for two to five years, losing each year a proportion, Norway spruce five years old still having 10 per cent germination. In trade, a germination percentage for spruce of 75 to 80; pine. 70 to 75; fir, 30 to 50; larch, 20 to 40, should be acceptable. Seeds are best kept in a dry, cool garret in tight bags or boxes, excluding the air as much as possible. All seeds require a short rest or after-ripening of two to four weeks before they are ready to germinate, and some, like the taxus and juniper, lie over, even in nature, for a year or more before they germinate. The latter should be prepared for sowing by macerating them, and removing the pulp in hot water, then mixing with sharp sand in bags, and by friction freeing the seed from the pulp. In the seed-bed somewhat more care is required than with most other species of trees. A thoroughly mellow, well-pulverized seed-bed of light loamy sand, possibly enriched with well-decomposed manure (cow-dung better than horse-dung) is required, the covering of the seed varying, according to size, from a mere sprinkling for larch to ¼ inch for the heavy-seeded pines. They may be sown as soon as the weather is settled, in northern latitudes the second or third week in May, best in rows not more than 6 inches apart, and preferably in dry weather, when the soil does not clog, for clogging or baking of the earth sometimes prevents seeds from germinating. Mulch between the rows with pine needles or sphagnum moss, or other fine mulch, to reduce necessity of watering and weeding. Conifer seeds need very little water for germination. The seedlings, on the other hand, for the first three months, until they have made their crown bud, need to be either kept well watered or else protected against the drying effects of sun and wind by shading, for which purpose lath screens are best. These latter must be lifted for airing after the sun is gone, especially in muggy weather, to avoid damping-off. For wintering, a covering with conifer branches or very clean meadow hay is advisable (the latter is likely to bring in weeds). For growing small quantities, the use of boxes, as described by Jackson Dawson, of the Arnold Arboretum, in Proceedings of the Massachusetts Horticultural Society, is highly commendable. In well-drained boxes, sow the seed soon after gathering, pile four or five deep in a pit or sheltered place, cover with boards, and when cold weather comes, cover up with leaves or hay. About the middle of April, move them into a place where they get the early morning sun. Keep the seedlings well watered and free from weeds, and shaded as described. Winter the seedlings in same manner as the seed-boxes, well covered up. They are ready for transplanting next spring, when they are making their first or second set of true leaves. Since pine and spruce seedlings take about seven to ten pounds of phosphoric acid, ten to twenty pounds of potash and fifteen to thirty pounds of lime, besides twenty pounds of nitrogen, per acre from the soil, for continuously used nurseries the addition of mineral materials in the shape of bone-meal and wood-ashes may become desirable. A large number of seedlings may be grown in a small space; thus 30,000 Norway spruce may be grown on a square rod, requiring about two pounds of seed. The quantity of seed sown depends, in part, upon the length of time it is expected to leave seedlings in the seed-bed, besides size and quality of seed; the quantities vary from one-fourth to one-half pound per 100 square feet if sown in drills, and the yield of seedlings will vary from 2,000 to 25,000 seedlings, according to species and seasons. Transplanting and pruning Conifers, like any other trees, may be transplanted at any time of the year, provided the necessary care is taken in moving the plant. This care is least required, as with other trees, in the fall and early spring, when activities of root and foliage are, if not at rest, at least reduced. Which of these seasons is preferable depends on the locality, and the dependent character of the season. On the whole, spring planting will probably be preferable in most parts of the United States which do not suffer from dry spring winds. In localities of the Southwest, which have commonly a dry spring followed by a rainy season in July, this latter time should be chosen. There is a belief that planting in August is specially favorable. There is no reason for this belief, unless favorable weather (a rainy season) follows. Conifers may be transplanted later than deciduous trees, even after the buds have started, excepting the larch, which buds out very early; with this species, fall planting may be recommended. Cloudy weather, rather than rainy or very dry, should be chosen, especially when transplanting into nursery rows. Young trees are naturally more readily and successfully transplanted than older ones, with which there is more difficulty in securing the whole root-system when taking them up. Since, however, the seedlings develop slowly for the first one or two to three years, they should be left in the seed-bed for that length of time, root- pruned, and then transplanted into nursery rows. Although those with a shallow root system, like spruces and firs; may be moved even when 30 to 40 feet in height, it is best, even for ornamental purposes, not to take them more than 3 to 4 feet in height. In forestry, one- to four-year-old plants, according to species, from 2 to 12 or 15 inches in height, are preferred for reasons of economy. Much greater care than with deciduous trees is necessary, when transplanting without an earth-ball, in keeping the root fibers from drying out; a large amount of loss in transplanting is explained from neglect in this respect. As soon as taken up, the roots should be immersed into a loam-puddle, or kept protected by wet sphagnum moss or canvas until set into their new place. The question of trimming when transplanting must be considered with more care than is necessary with broad- leaved trees, which possess much greater recuperative power. It should be confined to the smallest amount, smoothing bruised roots, and if for proper proportioning pruning at the top becomes absolutely necessary, shortening the leader rather than branches. Larch will stand more severe pruning than most other conifers. From the artistic as well as physiological point of view, it is barbarism to remove the lower branches, which the tree needs to shade its trunk and standing room, and often, when deprived of the same, will replace first before starting again, in its height growth. Attention should, however, be especially paid to preventing double leaders, which are detrimental to future form-development; cut them out as early as possible, preferably in the bud. Laterals may be somewhat shortened-in while standing in the nursery, to lengthen the time during which the lower branches are to persist. Breaking out buds is, as with all trees, the best method, provided the pruner has an eye for his business. Even in after-life, when pruning is performed to keep the tree shapely, the minimum use of the pruning-knife should be the rule. There are three marked periods in the development of conifers—the juvenile period, when the entire tree is a crown, branched symmetrically to the base, the perfection of symmetry; then follows the adolescent stage, when the lower branches die out, a period of unshapeliness; followed by the virile stage, when the straight, cylindrical shaft bears the crown at one-third or one- half of the upper length of the bole. The trimming during the adolescent stage requires most consideration. It is, in most cases, best to take off only the lowest, dying or dead branches, as it becomes necessary. In pruning, cut as closely as possible to the trunk, even cutting into the bark, also removing the swelled portion on which the branches are usually inserted, when the callousing will be more rapid and satisfactory in shape. If at this stage or at any time, the trees show trouble at the top by drying (becoming "stag-headed"), it is a sign that they suffer at the root from lack of moisture. Trimming off a few tiers of lower branches, loosening the soil as far as the ambitus of the crown, and mulching will largely correct this. If this proportioning of crown to root is not done, the tree itself will do it and not necessarily in desirable form. When used for hedges, the treatment is, of course, different. For such a purpose the shade-enduring species, spruces and hemlocks, are best, since they are capable of preserving a dense interior foliage, while the pines are bound to thin out. Enemies There are a number of dangers and damage from insects to which conifers are exposed. Drought and frost are most dangerous to seedlings in the seed-bed. These are obviated by proper location of the seed-bed (protection against sun and wind), by covering with a mulch of moss, straw, pine-straw or the like (which also prevents the heaving out by frost and the washing out by rain, to which young seedlings are liable). By shading and watering the danger of drought is overcome, although at the same time that of damping-off is invited. The cause of this disease, consisting in the reddening of the needles and their falling off, is a fungus which can be combated by spraying. Birds may be kept away from the seeds by mixing them with red oxide of lead, by lath screens, and the usual methods. Various fungi and insects, too many to mention, some polyphagous, others more or less specific, are at work during the various stages of development. A host of leaf-miners, saw- flies and caterpillars destroy the foliage, and weevils sap the young shoots. Bostrichi, or bark-beetles, mine under the bark, mostly of trees that are sickly from other causes; borers enter the wood of the boles. Tortrices bore into the base of leaders and cause them to break off. The best remedies against most of these are preventives, namely providing the trees with such chances of vigorous growth, or satisfactory soil conditions, that they are able to ward off or overcome the enemies. Otherwise, watching and destroying the enemies in time, and the usual remedies to kill them, may be employed. Literature: Veitch, "Manual of Conifers;" Carriere, "Traite des Coniferes;" Beissner, "Handbuch der Nadelholzkunde;' Fernow, "Care of Trees. B. E. Fernow. Transplanting large trees Moving large trees divides itself into two classes: First, with a ball of earth; second, with the earth dissected out from the roots with or without a ball remaining in the center. Start at or near the ends of the roots where they are 1 inch in diameter or less. In practice, this results in about 30 feet spread of roots on a tree 12 to 15 inches in diameter. An elm 18 inches in diameter on very thin gravelly soil was found to have a root 6 inches in diameter at 15 feet from the trunk, extending toward a horse- shed and cultivated field where it would get more food and water. A trench is dug to below the roots, which may be 1½ or 3 feet. An under-cut is made and the soil caved down by a picking bar or fork with round pointed tines. The earth and roots will be mixed at the bottom of the trench. The roots must be carefully picked up with the fingers, bound in bundles and tied out of the way. This operation is the point of greatest failure as it takes considerable time, patience and skill, to avoid breaking the roots. There are many chances to break a root after it has been carefully dissected out. The roots must be promptly lifted up or they will be broken by the shovel in digging out the loose soil at the bottom of the trench. The bundles must be untied and rearranged where the roots cross. This proceeds until a tree is dug in to a ball about 6 to 8 feet. The tree is then tipped Over by tackle, cleaving the roots from the subsoil. The amount of earth left in the center depends upon the strength of the truck, Character of the roads and power for hauling. To leave a mass of earth 6 to 7 feet wide. 15 inches deep, is practicable with two teams and 6-inch tires over hard dirt roads. Such a ball is helpful because there are more roots left undisturbed and they help support the tree during the first summer, especially if the ball is kept to the proper degree of moisture. Larger balls, 8 and 10 feet in diameter, 15 to 20 inches deep, can be carried only by more expensive trucks with much wider wheels, and with deciduous trees the advantage is slight as compared with carrying a full circle of roots 30 to 40 feet wide. The trees are readily picked up by the trunk which is protected by cushions and clasped by slats, and chains tightened by screws. A cradle is hinged at the front axle and tips the tree over in a horizontal position which is necessary on account of overhead wires and bridges. There are one or two screws about 9 feet long, 2½ inches in diameter. Tipping is accomplished by these screws or tackle or both. The roots on the lower side of the tree are tied back underneath the axle. In transporting, the roots are wrapped in straw and burlap. They can be exposed to the air for a day without serious injury, as roots ⅛ inch in diameter do not get dried out and killed in that time. In passing under wires, these can be lifted by a T-shaped pole and disentangled from the branches by proceeding a few feet at a time. Dangerous high tension electric wires must be handled by linemen employed by the electrical company. It is sometimes necessary to raise the wires or take them down and drive over them. In planting, the truck is drawn into the hole and stopped at such a distance from the center that the tree when swung over will be in the right position. The holes should be made of such a depth as to keep the roots as near the surface as possible. Allowance must be made for the bending of the downward roots below the center of the ball. The most frequent mistake is to get the tree too deep, especially the roots at the outside of the ball, which will often drop to the bottom of the hole and be 18 inches deep ; whereas when dug there were some at the surface, some 6 inches deep and a few 18 inches deep. After the tree is stood up in the hole by means of the tackle and screws, earth is packed under the center by packing- sticks. This is difficult and there are liable to be airholes left vacant. A stream from a hose will help to wash mud into these spaces. It is best to leave the bundles of side roots tied up while this is going on. Before the bundles of side roots are untied, the bottom of the hole should be filled up, if necessary, so that these are 2 to 8 inches below the surface. Spread out the side roots and cover with earth. Anchoring the tree is important. It is easily done by three or four anchor posts 4 feet deep with a crosspiece 3 feet long. Wires should be put through rubber hose and twisted around the tree. The tree is liable to settle, the anchor posts move, the tree lean and require straightening and tightening of the wires by further twisting. Pruning is important, made so by cutting back the tree from 2 to 8 feet all around. It is best to cut the most at the apex and the least at the sides, to make the shade as wide as possible. If cut back to an even outline, the tree will make a dense growth and look more solid the first year. If the thinning-out method is used, the thinning is liable to be too great in the center of the tree, as it is easy to reach, and the tree has to thicken up over a period of four years by making sprouts in the center, the outer branches remaining thin, especially if the tree is not fed and watered enough. Wrapping the trunk with straw may be necessary with thin- barked trees, especially in warm and dry climates. The bark is liable to dry out and die on the southwest side. The wrapping and anchors may be removed after two years or more. A mistake is often made in choosing trees within two miles, whereas, the area to draw upon is over fifteen or twenty miles radius which will contain much better trees, the time on the road being a comparatively small item in the total cost. Trees are often chosen which are growing on thin or rocky soil or in swamps saturated within 6 inches of the surface, both giving much less amount of roots than trees in a friable soil 3 feet deep. In a country of hills and valleys, the best trees may often be found in terraces or benches above the river bottom or in the river bottom if drained to allow roots to be 3 feet deep. Trees are often chosen which are too old and have made a short, slow growth. It is better to move a young tree 35 feet high, 12 inches in diameter, which is growing 1 foot a year, than to take a tree the same size, twice as old, growing 3 inches a year. The roots on the latter will be longer and less flexible. Each will live and crow rapidly if given favorable conditions. A mistake is often made in choosing trees which are crowded or in thick forests. The latter may appear to have low branches. These branches are weak and liable to die. Trees of species difficult to move and trees about the moving of which little is known are liable to be chosen. Trees which move readily are those of soft wood, rapid growth, usually native in moist soils, as maple, elm, linden, poplar, locust, catalpa, horse - chestnut, birch, apple and pin oak. The following are trees about which less is known: Pepperidge, sassafras, plane, chestnut, beech, tulip, white oak, black oak, liquidambar, ailanthus, hickory, walnut and ash. The chestnut, beech, magnolia, tulip tree, black oak and walnut do not indicate by their behavior when small that they are readily moved. It is to be presumed that the ailanthus and ash are easily moved. No species has proved itself impossible to move. It is merely a matter of getting the right proportion of roots and top and nursing the tree through the convalescence until it has reestablished itself. In moving trees it may be better to move three trees 8 inches in diameter, 35 feet high, than one tree 16 inches in diameter, 35 feet high. From three smaller trees there will result a wider mass of foliage, and it will be easier for those not equipped with large tree-moving apparatus to handle the three smaller trees. If the earth is dissected out from the roots, two trees 8 inches in diameter could be carried by one team. They can be loaded on a low stone truck or handy wagon, the trunks of the trees resting on two benches which lessens the breakage of roots and top. Trees can be loaded by the men, the tree being tipped over on the truck which stands beside the hole. The tree is shifted into position by the men lifting on the trunk, or it may be lifted by a shear pole derrick or single pole. Many people hesitate about moving large trees and wait fifteen years for a result they could easily secure in this manner, by collecting wild trees in the vicinity. Root-pruning a year in advance may aid in moving a tree, but is not essential. If a trench is to be dug at a radius of 4 feet all the way around a tree 10 inches in diameter, it is better to move the tree with a wider spread of roots and take good care of it. A root- pruned tree is likely to be neglected and suffer for moisture. The tree can be root-pruned three-quarters of the way around for one season and perhaps be in better condition for moving. This is more likely to be beneficial with a tree with long coarse roots and with few fibers in the center, like a black oak. A mistake is frequently made in assuming that a ball of earth is all that is essential, regardless of the amount of fibrous roots in the ball and of its area to gather rainfall as compared with the top. Frequently trees dug around the roots cut off at a diameter of 10 feet, have the tree-mover sent for when they should have a spread of roots of 30 feet. The ball-of-earth method with deciduous trees usually consists in carrying a ball of earth 7 to 9 feet in diameter with trees 10 to 18 inches, on a low truck consisting of a platform hung under four heavy wheels, the tree being lashed fast to a collar and pole on the rear axle, and pulled over to the rear and then the platform chained fast to the rear axle. The roots outside the ball are usually cut off. With elm trees carrying a slender top this method succeeds, although the trees are often slow in recovering. It succeeds with maples, but they are likely to grow slowly or die back until the tree reestablishes a balance, after several years. Deciduous trees can be moved in midsummer in full leaf. Norway maples 7 inches in diameter were well watered to fill them with sap; the next day they were dug with roots spreading 15 feet, leaving a ball of earth 5 feet in diameter in the center. The tree was tipped back and a platform or stone boat moved under, on which it was moved. After planting the trees were watered about four times, once in ten days. The ball of earth became dry very quickly. The bundles of outer roots did not send out fibers for about two weeks. Trees with less fibers in the center would probably not succeed so well. See also Drainage and Evergreens for further discussion. Types of insect injury to trees Trees of all sorts are liable to injury by many kinds of insects, so many indeed that it is difficult to present a satisfactory account of their depredations without going into great detail. A few insects stand out preeminently, however, among the more common and widespread tree pests and a selected series of these will serve as examples of the various ways in which the trees may be injured by these animals. Destructive forest- or shade-tree insects may be grouped into two classes, according to the way in which they feed, based on the fact that one series feed by chewing and consuming the tissue of the trees, while the members of the other class derive their nourishment from the juices or sap of the trees which they suck out by means of needle-like sucking mouthparts. Most insects pass through three, or at least two, preparatory stages, very different from the adult, before they reach maturity. They hatch from eggs deposited by the adult female, as larvae (grubs, caterpillars, maggots, and so on) and in this larval stage feed till they attain their full size. The larval stage is, therefore, the most destructive one. When full grown, the larva usually changes to a resting condition or pupal stage (chrysalis), and during this time does not feed. Finally the adult appears and the life-cycle is complete. Many insects undergo a single generation every year, but a number grow more rapidly, producing several broods each season, while a few require two years or more to mature. Insects provided with chewing mouthparts may feed on the leaves and are then known as defoliators; or they may feed on the bark, cambium, sapwood, heartwood, or roots, in which case they are known as borers. Caterpillars, beetle grubs and saw-fly larvae are the most important insects of the latter kind. Among the insects with piercing mouthparts, some suck the juices of leaves, while others affect the twigs and branches, or even the roots. Plant-lice and scale insects are the most important insects of this kind. Methods of destroying tree-pests There are five widely different methods of destroying insects which injure trees, and the selection of an appropriate method must depend primarily on the feeding- 'habits of the species to be dealt with. (a) All defoliators, such as caterpillars (Fig. 333), saw- fly larva; (Fig. 334), and those beetle larvae that feed externally upon the leaves, are best killed by the application of an arsenical poison (Figs. 335, 336). This is applied preferably by some sort of a spray-pump that throws a fine mist or spray of water in which the arsenical has been mixed. Such spraying machines may be obtained in sizes to suit any needs, from hand-pumps holding a quart of liquid to power sprayers equipped for spraying extensive woodlands thoroughly and rapidly. The most satisfactory poison is arsenate of lead, an insoluble arsenical which can be mixed with water in the proportion of six to ten pounds to each 100 gallons of water and sprayed upon foliage without danger of damage to the leaves. It is sold commercially as a _ . white paste and is easily handled. This substance is far superior to paris green, london purple, and the like. It should be applied only in sufficient amount to show after drying as whitish specks upon the surface of the leaves. (b) Plant-lice, since they feed by inserting their beaks into the tissues of the leaves, and other soft parts, are not affected by arsenicals and must be destroyed by spraying with what is known as a contact insecticide, one that kills through the application upon the surface of the insect's body. The most generally used, and one of the best contact insecticides is kerosene emulsion. This is prepared by dissolving half a pound of common laundry soap in one gallon of hot water and then adding two gallons of kerosene while stirring or churning the mixture violently. The creamy mass thus formed thickens on cooling and must be diluted with nine times its volume of water before being sprayed upon the plants. Scale insects feed like plant-lice, by inserting their delicate beaks into the tissue of the tree and sucking out the sap, but usually occur on the thin bark of the branches and twigs rather than on the leaves. Each insect secretes a scale-like covering beneath which it lives while growing, and, even when adult, the female never leaves her position beneath the scale. As the scaly covering is of a waxen nature, these insects are not so easily destroyed by contact insecticides as are plant-lice, although kerosene emulsion is sometimes effective, especially in the case of young insects which have not yet secreted a thick scale. Many older or more resistant scales cannot be destroyed in this way and they may be killed when the trees are in a dormant condition by a spraying with lime-sulfur wash prepared as follows: Water, forty gallons; fresh lime, twenty pounds; flowers of sulfur, fourteen pounds. These are boiled together for one hour and then applied as a spray to the branches and twigs. This wash should never be sprayed upon trees when in leaf. (c) Bark-beetles.—These are small insects that live during the larval stages beneath the bark of the trunk and branches of trees. The parent insects enter the bark and excavate a small tubular gallery through the cambium or inner bark. Along the sides of this, the eggs are laid and the developing larvae eat out sinuous burrows through the cambium. They thus interfere with the sap-flow and cause a general weaking or even death of the tree. Bark-beetles are liable to attack sickly or dying trees, and the only feasible method of lessening their depredations is to remove and burn such trees or branches as are affected, in addition to improving in all possible ways the conditions under which the tree is growing, bearing in mind that healthy trees are much less likely to be troubled by these insects than are weak, poorly nourished ones. (d) Wood-borers.—The larvae of certain beetles and moths subsist upon the woody tissues of trees, excavating galleries through the wood of both living and dead trees. Such larva; are usually whitish, often with brown head and have powerful jaws, by means of which they can cut through the solid wood. They may attack trunk, branches, or twigs, some working in the sapwood, others in pith, while a few feed mainly on the heartwood. Insects of this kind are the most difficult to combat as they feed where they cannot be reached by means of insecticides during the greater part of their life. Due to their concealed position, they are not so readily noticed and may frequently cause irreparable damage to trees before their presence is recognized. Besides cutting out the individual larvae or destroying them in their burrows by means of a piece of wire, no general method of destruction can be recommended. It is important, however, to maintain the trees in as healthy condition as possible, and to remove all dead or dying timber in order to reduce the number of breeding-places for the insects. (e) Leaf-miners.—To this class belong some of the members of several different groups of insects, certain small moths, a few saw-flies and a small number of flies and beetles. All of the leaf-miners are very small insects whose lame feed upon the parenchyma of the leaf, leaving intact the upper and lower epidermis. In this position they are protected from most sorts of insecticides, although in some cases, spraying with a contact insecticide containing some tobacco compound in combination with soap may be efficacious. One formula recommended is: water, 800 gallons; nicofume, or "blackleaf 40," one gallon; laundry soap, thirty-two pounds. Ordinarily, leaf-miners do not present a serious menace to trees, but the presence of their blotch-like or serpentine galleries, which show as faded areas, often greatly disfigure the leaves. Some of the more important shade-tree pests A. Defoliators. The tussock moth, Hemerocampa leucostigma (Fig. 337), is perhaps the most abundant caterpillar on trees, particularly in thickly settled districts. The eggs are laid in the fall in white fluffy masses the size of a dime on the trunks of infested trees and hatch in the early summer. The larvae bear several pencils of long black hairs placed at each end and have four brush-like tufts of pale yellow hairs above, with a bright red head. These pupate early in July in crevices in the bark and the adults soon emerge to lay the eggs for a second generation of caterpillars which will mature before fall into moths that deposit the over-wintering eggs. The female moth is without wings and lays her mass of eggs on the bark where she emerges from her pupa case. These caterpillars feed on all sorts of trees except evergreens, but seem to be most destructive to maple, elm and American linden. Two related caterpillars have been imported from Europe into Massachusetts, the gypsy moth and brown-tail moth, and although these are at present confined to that neighborhood, they will undoubtedly become widespread before many years have elapsed. The gipsy caterpillars feed on many kinds of trees, preferring oaks; they may be recognized by a double line of round spots down the middle of the back, blue, followed by red ones. Their life-cycle is like that of the tussock moth, except that there is only one generation passing the winter as a mass of woolly, dull ochre-yellow eggs attached to the bark. The brown- tail is a brownish caterpillar with white spots, passing the winter in small woven silk nests containing many caterpillars. The nests are attached to the tips of the twigs of infested trees. Orchard trees suffer most severely from thus species, although all sorts of broad-leaved trees arc attacked. Another common caterpillar of very different habits is the American tent-caterpillar, Malacosoma americana. This is an inconspicuous brownish moth which over-winters as a band-like mass of eggs placed around twigs of cherry and a number of other trees. These hatch in very early spring and the larvae spin silken nests in email forks of the branches from which they crawl out to feed upon the opening leaves. They mature in early summer and the eggs are laid in midsummer for the next season's brood. The bag-worm, Thyridopterix ephemeraeformis, is a defoliator at times very destructive, although each larva in his dependent bag does not have a wide range of operations. Fig. 338. Hand-picking and arsenical sprays are the remedies. The caterpillars of the mourning cloak, Euvanessa antiopa (Fig. 339), are a very common pest of elm and other shade trees. They are black, coarsely spiny caterpillars with red spots along the back, and feed more or less in colonies, usually defoliating single branches at a time. The butterfly passes the winter as an adult, appearing in very early spring, and laying its eggs in May. The caterpillars from these eggs become full-grown before July, and the butterflies of another generation appear in July to lay eggs which will give rise to the hibernating butterflies of the next winter. A common saw-fly which occurs on willows is the American saw-fly, Cimbex americana. The larvae are much like the defoliating caterpillars of moths and butterflies in appearance and feed in the same way, destroying the entire leaf-tissue. The larva; are pale green, with a blackish line down the back. When mature, they descend to the base of the tree, where they spin parchment-like brown cocoons in which to pass the winter on the ground among fallen leaves. In the spring, they transform and the adult saw-flies deposit their eggs singly in slit-like cuts made into the tissue of the leaf. Pine trees often suffer from the depredations of saw-fly larvae of the genus Lophyrus which devour the needles, near the bases of which they later spin their small cocoons. Many saw-fly larva; feed only on the leaf from one side, leaving the epidermis of the other side intact. Arsenical sprays for the destruction of such species must be directed against the side of the leaves attacked, usually the under surface. Among defoliating beetle larvae, the imported elm leaf beetle, Galerucella luteola (Fig. 340), is probably most important. This occurs only in the eastern states but is gradually spreading into the middle West. The small, yellow, two-striped adults live through the winter and deposit their bright yellow eggs in small masses on the under side of elm leaves in early spring. These eggs hatch into black and reddish slugs which feed on the under surface of the leaves, leaving only the veins and upper epidermis. The leaves then dry up and may fall off. The larva;, now changed to a yellow color, descend to the surface of the ground to pupate and soon emerge as a summer generation of beetles. There are two or three annual broods, according to the latitude. Plant-lice and scale insects. There are many kinds of plant-lice (Fig. 341), but all pass through very similar life- cycles. In general, this is as follows: the winter is passed as a large, shining elongate oval egg attached to a twig or branch. This gives rise in the spring to a soft-bodied wingless female aphid that gives birth to living young aphids, which in turn reproduce in the same way. These suck the juices from leaves, petioles or tender twigs and thus sap the vitality of the tree. In addition, the leaves may be disfigured by a sticky substance, known as honey-dew, secreted by the insects. In the fall, both females and winged males are produced and the female lays a single winter egg. On account of their method of reproduction, plant-lice multiply very rapidly, especially in damp seasons. Some species have a more complicated life-cycle, producing winged individuals in the summer which migrate to another food-plant, later to return in the fall to the original one. A few plant-lice living in colonies produce galls, curled leaves, or other malformations on the leaves or twigs of infested trees. Scale insects exhibit a greater variety in their seasonal history; some pass through a single generation each year, while others multiply more rapidly, passing through a number of generations annually. The winter is sometimes passed in the egg state, but more commonly as a partly grown insect. One of the commonest and most destructive scales is the oyster-shell scale, Lepidosaphes ulmi. This occurs on the thin bark of a great variety of trees, appearing as a very small, elongate, flattened body, pointed at one end and rounded at the other, with the upper surface more or less distinctly ridged in a transverse direction. There is a single generation annually, the females maturing in late summer and depositing a mass of eggs which remains beneath the scale through the winter, hatching in the spring and producing full-grown insects by midsummer. Sometimes this species is so abundant that the smaller branches appear as if covered by a gray incrustation. The San José scale, Aspidiotus perniciosus, is another important scale, which has been introduced into many parts of the United States. It is very destructive, primarily to certain orchard trees, but injures many thin-barked shade trees as well. The scale is very small, round in the female and oval in the male, with a minute nipple-shaped projection near its center. The females do not lay their eggs till the young insects are ready to hatch, so that they practically produce living young. These develop rapidly, five or six broods maturing each season of which the last hibernates in the half-grown condition. In mass, the scales form a gray, granular crust, covering the branches and twigs. In some parts of the country, maples grown for shade trees suffer great injury by the cottony maple scale, Pulvinaria innumerabilis. This scale is most conspicuous on the twigs in early summer, at which time the females are depositing their eggs. It then bears a tuft of fluffy waxen substance resembling a bit of white cotton. The young scales appear soon after, when they migrate to the leaves and feed till early fall before returning to the twigs, where they finally pass the winter in a half-grown condition. Practically all sorts of trees suffer at times from scale insects, of which there are many kinds. The common forms are divisible into two groups, the soft scales and armored scales. The former are soft and convex like the cottony maple scale, in which the "scale" is the back of the insect itself; the latter are usually smaller, like the San Jose scale, in which the "scale is a separate waxen cover secreted by the insect. c. Bark-beetles. These insects are small black or brown beetles that live in the larval stages beneath the bark, feeding on the inner bark and cambium, and all have very similar habits. The parent beetle enters the bark through a small hole about the size of a pencil-lead, and excavates a single primary or egg-gallery through the cambium, usually grooving the sap wood. This tunnel varies from one to several inches in length, and along its sides the female cuts out little pockets, in each of which an egg is laid. On hatching from the eggs, the larvae excavate individual mines usually more or less perpendicular to the egg-gallery. When full grown, the white legless grub-like larvae pupate in cells excavated in the bark, from which the beetles emerge by chewing out a circular tunnel to the surface. Trees from which beetles have emerged appear as though the bark had received a charge of buck-shot, from the presence of the small circular emergence holes. Some forms, like the genus Denroctonus, attack fine healthy coniferous trees and kill much valuable timber, but shade trees are more commonly attacked by the species that live in the bark of deciduous trees, more particularly those that are in a sickly condition. A common form is the hickory bark-beetle, Eccoptogaster quadrispinosa, that attacks hickories. The beetles appear in June and July, to excavate the primary galleries which extend vertically for an inch or two. Forty or fifty eggs are placed in notches on the sides and the larvae bore out at right angles, thus girdling the cambium and weakening or killing the branch. This species undergoes only one generation annually, although some others pass through two or more each season. There are many other kinds, all scarring the bark or surface of the wood in a similar way. D. Wood-borers. The larvae of many beetles and moths, and of a few wasp-like insects, injure trees by excavating their food- burrows through the solid wood. Birches, grown for shade or ornamental trees, often suffer great injury from the presence of a flat-headed borer, the bronze birch-borer, Agrilus anxius. The small elongate bronze green beetles appear in May or June and deposit their eggs on the branches, at first near the crown of the tree. The larvae penetrate the bark, beneath which they cut irregular flattened galleries till grown, when they cut out cells in the wood in which to pass the winter before emerging in the spring. The upper parts of the tree suffer first and begin to die, and the following year the larvae appear nearer to the ground. Chestnut is attacked by Agrilus bilineatus, the two-lined chestnut-borer. Most other kinds of trees suffer similar injury from related beetles, many of which multiply also in dead trees and stumps. Another flat-headed borer, the larger flat-headed pine-borer, Chalcophora virginiensis (Figs. 342, 343), extends its flattened burrows deep into the wood of the tree, a method of feeding exhibited by many borers of this group attacking deciduous trees also. The larvae grow to a length of 2 inches before cutting out their transformation cells in the bark. Round-headed borers are similar in habits, but belong to another family of beetles in which the larvae are less distinctly flattened near the head and excavate more nearly cylindrical burrows. One of our commonest species is the locust-borer, Cyllene robiniae, which attacks yellow locust trees. The elongate medium-sized black beet- les, with brilliant yellow markings, appear in the early fall to deposit (Natural size.) their eggs on the bark of the trees. The eggs soon hatch into larvae which feed for a time and then over-winter in a small cell beneath the bark. Next year they bore through the living wood and transform in August to beetles. This species can destroy healthy locust trees rapidly and is a very serious pest wherever the tree is grown. All infested trees should be pruned or felled and burned to destroy the larvae, in the fall or winter. Sugar maples suffer from a similar insect, as do practically all sorts of trees. White pine trees are commonly deformed by the larvae of the white-pine weevil which feed exclusively beneath the bark of the terminal shoots of young trees of this species. (Fig. 344.) The carpenter moth, Prionoxystus robiniae, is a large common mottled gray insect with pale yellow black-headed and black- speckled larvae 2 inches in length, that bore in the branches of many kinds of trees. Oak suffers most, but maple, ash, locust, willow and cottonwood are often infested. The moth lays its eggs on the bark late in the summer, and for two or three seasons the larvae feed on the wood, cutting large circular burrows. They transform in the burrow, the pupa working its way partly through the bark for the eclosion of the moth. The brown pupacase may then remain projecting from the mouth of the burrow for some time. A related European insect, the leopard moth, Zeuzera pyrina, has recently become abundant along the northern Atlantic coast region, attacking elm and all sorts of other trees and shrubs. It feeds in the same way and bids fair to become one of our worst shade-tree pests. The larvae of many other moths injure trees in a more or less similar way. The pigeon horn-tail is a large cylindrical yellow- brown and black insect with grub-like larvae that bore in elm, maple, and other trees. The females insert their eggs deep into the tree by means of a needle-like ovipositor. They frequently fail to extricate the ovipositor and may be seen dead, but still attached to the tree trunks. E. Leaf-miners. Small larvae belonging to several orders of insects live as miners in leaves, the most abundant forms often greatly disfiguring the foliage of affected trees. Deciduous trees of all sorts are affected by the leaf- mining larva; of various small moths, but it is very difficult to distinguish the different species without minute study. Oaks are particularly susceptible and are commonly disfigured by the sinuous or irregularly rounded mines that appear as pale streaks or blotches. Even pines suffer from such larvae, which enter a needle and eat out the tissue, causing the tip to dry and become yellow. Occasionally insect larvae cause malformations or swellings of the leaves or twigs, known as galls. (Figs. 345, 346.) Yellow locust suffers from a leaf-mining beetle larva. Odontota dorsalis, that eats out almost all of the leaf parenchyma, causing the leaves to dry and shrivel. Related species affect oak and basswood. Members of another family, belonging to the genus Brachys, also mine in leaves of oak, chestnut, and so forth. One leaf-mining saw-fly is of considerable importance, Kaliofenusa ulmi, the larvae of which eat out the parenchyma of elm leaves between the lateral veins, causing them to assume a seared appearance in spots (Fig. 347). Another closely related species mines in the leaves of the hawthorn (Crataegus). The latter may be satisfactorily killed by a spray of tobacco-water, but the species on elm is more resistant. The larvae of these species enter the ground later in the summer to spin their cocoons. C. T. Brues. Some types of tree diseases Disease in plants is the result of any derangement in the normal form, structure or physiology of the organism. The disease condition becomes manifest by different symptoms, according to the nature of the disorder. Such symptoms as stag-head, cankers, leaf-spots, witches' brooms, and so on, are examples of the effect produced in the tree by some disease-producing agent or combination of agents. The variety of functional disorders alone that may arise in trees is large. Such causes as insufficient or excessive soil water, malnutrition, excessive heat or cold, or rapid variations in temperature are capable of producing effects called physiological diseases. On the other hand are those diseases that are produced by the activities of parasites, such as certain of the fungi, and bacteria. Accurately to place a new or little-known disease in one of these two classes is often difficult for the expert, even after much study. There is relatively less known concerning the physiological diseases of trees than of those caused by parasites, not because of their less importance so much as of the difficulty of studying them. It is to be deplored that the diseases of forest, shade and ornamental trees have not received their due share of study and investigation by pathologists. How fungi cause diseases of trees. The fungi consist of a group of plants that do not contain chlorophyll, upon which all green plants depend for the synthesis of carbohydrates. Consequently, not being able to manufacture their own food, the fungi must secure it from their environment, by dissolving and utilizing organic materials from dead or living plant or animal bodies. By far the vast majority, luckily, belong to the class of scavengers which attack dead organic material and utilize it for food. These forms are called saprophytes. Other species of the fungi attack living plants and, through their activities, produce the disorders that are termed diseases. These are known as parasites or pathogens. In brief, the general action of the fungi that cause tree diseases is as follows: The fungus exists in two stages, the vegetative and the fruiting. The vegetative stage consists of a mycelium, which is an aggregate of long much-branched microscopic threads of fungous cells. This mycelium penetrates and grows in the body of the tree, extracting nutriment from it by dissolving the different structures it can utilize. In this process the tissues of the tree are destroyed and the fungus obtains food for its further development. In time, after sufficient food has been stored in the mycelium, the fungus forms its fruiting bodies. In the case of the larger number of the heart and sap-wood rots, this fruit body consists of a shelf-like or toadstool-like structure on the exterior of the tree. In these fruiting structures are borne millions of microscopic spores or seeds of the fungus, which are distributed largely by the wind. If by chance one of these spores finds lodgment on an exposed wound in the bark of a tree which it is capable of infecting, it will under proper conditions germinate, producing a mycelium that will penetrate the tissues of the new host. Seedling diseases. The young seedlings in the nursery beds are often attacked by certain soil organisms that cause a decay of the stem at the surface of the ground, allowing the plant to wilt and fall over. This type of disease is called "damping off;" in many cases it is caused by the fungus Pythium de Baryanum. This disease is largely induced by very moist soils, a moist atmosphere, high temperature, and little ventilation. By growing seedlings in light sandy soils, well watered but not excessively, and by aerating the beds well to reduce the humidity of the atmosphere around the plants, this trouble is practically avoided. Soils in which it has once occurred should be abandoned, however. In greenhouses in which this disease is often troublesome and the precautionary measures mentioned above difficult to maintain it may be necessary to sterilize the soil with formaldehyde or by steam heat immediately before sowing the seed. Leaf diseases. Very little serious damage is caused by most leaf diseases of trees other than the unsightly appearance produced. There are a few leaf diseases, however, that are of more or less importance in the United States. Conspicuous among these is the anthracnose disease of oak and sycamore leaves, caused by the fungus Gnomonia veneta. Throughout northeastern United States in recent years the plane-tree (Platanus occidentalis) has been almost universally affected and the trees often completely defoliated before the first of July. Early in the season the disease becomes manifest by the production of rapidly enlarging brown blotches which are usually produced along the veins of the leaf. If examined closely, the numerous spore clusters can be seen. These clusters are composed of innumerable microscopic conidia which serve for the dissemination of the fungus. The twigs are commonly affected also and on these, as well as the fallen leaves, the fungus winters over. The same fungus produces a similar disease on oaks, especially the white oak, and is often epidemic in certain regions. As a measure of prevention, all fallen leaves and twigs from diseased trees should be carefully collected and burned. All diseased twigs should be pruned off and burned. If desirable, the trees may be sprayed with standard bordeaux mixture from the time the leaves begin to unfold, at periods of two or three weeks until the first of July. The tar-spot disease of the maple caused by Rhytisma acerinum is a conspicuous disease but seldom causes serious damage to the tree. The diseased spots appear as blotches of tar on the upper surface of the leaves. Burning the diseased leaves will materially lessen the chances of attack the coming year since the pathogen winters in them. Maple trees, at least in the northeastern states, have suffered during the past few summers from a physiological trouble called leaf-scorch. The leaves of one side or the whole of the tree turn brown between the veins and finally dry up. This disease has been ascribed to over-transpiration of the leaf-tissues at a time of year when the roots cannot furnish enough water to the tree to compensate the loss. Thus the leaf-cells are killed by desiccation and the brown blotches appear. It is advised that artificial watering during hot, dry weather will materially lessen the severity of the trouble, especially under city conditions. Canker diseases. A diseased condition of the limbs or trunk of a tree that results in the death of an area of the bark is termed a canker. These cankered areas maybe either sunken or enlarged, and the terms necrotic and hypertrophy cankers are used respectively to designate these characters. Not all cankers are produced by parasitic organisms; some are the result of malnutrition, winter injury, sun-scorch, insects, and the like. By far the worst epidemic disease of trees in America is the chestnut-canker now prevalent in many of the eastern states. In all, a total loss of $25,000,000 has been ascribed to this disease between the time it was first noticed, in 1904, on Long Island, and the year 1912. The cankers produced on the chestnut are caused by the fungus Endothia parasitica. Fig. 349. At present, the question of the origin of this disease in the United States is undetermined. The fungus works rapidly in the bark and sap-wood, killing the tissues. Fruiting bodies of two types are formed on the diseased bark, a conidial stage that appears as long yellow tendrils of gelatinous matter and the reddish yellow to dark brown cushion-like stromata that contain the ascospores. These latter spores are ejected in large numbers at every rainy period throughout the spring, summer, and fall and are carried by the wind, readily causing new infections. On the individual tree, the fungus is rapidly spread by the washing down of the conidia into wounds in the bark. The cankered areas soon cause the death of the parts above by girdling the limb and, in most cases, complete death of the tree follows in two or three years. The state of Pennsylvania has taken steps to eradicate this disease by seeking out diseased trees and compelling owners to cut all affected trees in the western half of the state. The extremely virulent nature of the disease, however, has led more conservative pathologists to question the advisability of expending large sums of money with so slight a chance of ultimate or complete success. The problem of saving individual trees in affected regions has not been solved. The very nature of the disease precludes spraying, and tree surgery methods have not given anything more than temporary success. Incipient cankers are so difficult to locate and, by producing conidia when only three or four weeks old, serve to spread the fungus so rapidly over the tree that human efforts so far have failed. Rust disease. The most destructive and important rust diseases of trees are those caused by different species of the Peridermiums on coniferous trees. These rust fungi attack the needles, twigs, or limbs of coniferous trees, often producing defoliation or complete death of the tree. Notable among these diseases is the white-pine blister-rust caused by the Peridermium stage of the fungus Cronartium ribicola which has its Cronartium stage on species of currants and gooseberries. The fungus is not native to this country but has recently been imported from Europe. In Europe the disease has practically exterminated the white pine (Pinus Strobus) m many localities, and in this country the danger of a similar destruction of this species is now being faced, if the fungus acts with the same virulence as in its native environment. In 1912 the Federal Board of Horticulture placed a quarantine on most of the countries of Europe, which prevents anyone bringing white pine trees from these countries into the United States. The fungus attacks white pine from one to twenty years old, the mycelium growing in the bark and usually producing a swelling. The orange-yellow fruiting bodies burst through the bark in one to five years after infection. The spores from the pine can affect the gooseberry or currant leaves only. On these hosts other kinds of spores are borne in the fall which can infect the white pine only and thus the yearly cycle is completed. The black currant (Ribes nigrum) is by far the most virulently affected in this country, and it is advised that plants of this species are therefore extremely dangerous to the white pine industry and their culture should be discouraged. By keeping currants and gooseberries at least 500 feet away from white pines, a partial safeguard is provided against the passing of the fungus from one host to the other. All plants affected by this fungus should be immediately destroyed. Witches' broom diseases. Excessive branching at any point on a limb, forming a compact cluster of short stubby branches, is often caused by numerous agents, both insect and fungus, as well as by the mistletoes. In the South, especially, trees of many species are disfigured by these witches' brooms caused by the American mistletoe, Phoradendron flavescens and related forms. In the northern states the dwarf mistletoe, Arceuthobium pusillum (Fig. 351) causes similar brooms on the black spruce (Picea Mariana). Witches' brooms on red cedar (Juniperus virginiana) are caused by the rust Gymnosporangium nidus-avis. Root diseases. The principal root disease of trees that is widely distributed throughout the United States is that caused by the mushroom Armillaria mellea. The mycelium of this fungus grows in the soil on decaying wood as a saprophyte, but can also become parasitic, killing trees over large areas. Almost any of our indigenous trees may be affected with this disease. Fruit trees often suffer in certain regions. The mycelium penetrates the roots and grows in the bark and wood, working up into the base of the tree. The destruction of the root- system is so rapid, however, that two or three years after infection the tree often dies, before the fungus has spread any great distance up the trunk. In the older decayed parts of the root and in the soil, the mycelium is aggregated into long black, flattened strands called "rhizomorphs," or more commonly termed, , "shoe-strings." In the case of coniferous trees, an abundant exúdate of resinous sap occurs at the base of affected trees, which forms the surrounding soil into a cake. The disease may be recognized by the gradual yellowing of the foliage, decay of the roots, presence of the "shoe-strings" in the soil, and the appearance of the honey-yellow mushrooms around the base of the tree. No practical method of treatment is known. Diseased trees and the mushrooms should be destroyed. Other soil organisms may enter through wounds in roots and cause diseases. Such a disease may, after becoming established in the roots, continue to spread up the trunk. Thus wounded root-systems are as dangerous a source of infection as wounded branches. Roots often suffer from winter injury largely because the wood ripens from the top of the tree downward, and when severe conditions are undergone early in the winter before the new wood of the roots has ripened, it is killed. The above text is from the Standard Cyclopedia of Horticulture. It may be out of date, but still contains valuable and interesting information which can be incorporated into the remainder of the article. Click on "Collapse" in the header to hide this text.

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References

• Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963

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