|Standard Cyclopedia of Horticulture|
Viola (classical name). Violaceae. Violet. Pansy. Usually perennial herbs with attractive spring or early summer bloom, and well adapted for colonizing in grounds and one species for forcing; in the pansy group, many species are handsome winter annuals or biennials; and in the Andes and the Sandwich Islands, and in southern Europe shrubby species occur, but they are scarcely cultivated. See Violet.
Either stemless, bearing lvs. and 1-fld. scapes from the crown of the rootstock, or stemmed with manifest internodes between the lvs., from the axils of which arise 1-fld. peduncles: fls. usually of two kinds, those of spring with showy petals (Fig. 3935) and those of summer with petals rudimentary or lacking—fls. never opening but self-pollinated within the closed calyx (cleistogamous). (Fig. 3936.) The showy fls. of spring are 5-merous as to sepals, petals, and stamens, irregular and novel in structure as though contrived to prevent self-pollination; sepals nearly similar, persistent on the fr.; the lower petal of the nodding fl. spurred, the other 4 in 2 unlike pairs, the petals in each pair symmetrically alike; stamens short and included, the anthers more or less coherent in a ring about the style, 2 of them with nectar-bearing appendages projecting backward into the spur: fr. a caps. with several (up to 60) obovate seeds; caps. when ripe splitting into 3 boat-shaped valves with thick rigid keels; as the thin sides of the valve dry and contract the seeds within are more and more pinched, until they fly out, one or two at a time, to a distance often of 9 ft.: later cleistogamous fls. in some of the stemless species not growing in wet ground are borne on short horizontal peduncles concealed under soil and leaf-mold until the seeds are ripe, when the peduncle lengthens and lifts the caps. into the air, where it scatters its seeds as did the earlier caps. (Fig. 3936.) See Rhodora, vol. vi, plate 50, for cleistogamous fls. and frs. of 6 other species.—Probably 300 species widely distributed in the N. and S. Temp. zones of both the Old World and the New, of which about 80 species are native to N. Amer. north of Mex.
The classification of the wild violets into species was for many years a perplexing task, because students of the genus failed to recognize the fact that all closely allied species freely hybridize in nature. But in 1900 the important discoveries of Mendel became generally known to biologists, and gave rise to the new science of genetics. With a better understanding of the laws of inheritance that determine the characters of offspring from unlike parents, it is practicable in a genus like Viola to discover what forms are proper species and what are hybrids or the offspring of hybrids. Some of the tests employed by the specialist in Viola may be briefly indicated as follows: (1) The hybrid is notably intermediate in its characters between two well-known species found in the same vicinity. (2) The hybrid usually shows great impairment of fertility, 50 to 100 per cent of the ovules being aborted, but a marked increase in vegetative vigor. (3) The pollen-grains of most hybrids are seen under the microscope to be largely shriveled and functionally impotent. (4) The hybrid is found to be unstable in sexual reproduction; that is, the offspring of the self-fertilized hybrid are more or less unlike the parent and unlike each other; the offspring of pure species are not thus unlike.
By experimental cultures extending over twelve years, the writer has ascertained the existence of about eighty spontaneous hybrids among the violets of eastern North America—that is, more hybrids than there are pure species. In Wilhelm Becker's systematic treatise on the violets of Europe (published in 1910), eighty-three hybrids are reported among the one hundred and two species there recognized. Any reader caring for the details of the work on American violets will find a dozen or more papers in Rhodora and in the Bulletin of the Torrey Botanical Club (1904-1913); see also Science, June, 1907, and American Naturalist, April, 1910.
Violets are easily grown if an effort is made to imitate the conditions under which they naturally occur. They usually require abundant moisture and partial shade, and a light covering of fallen leaves or evergreen boughs in winter. The habitats are various: some are wood species, others from bogs or borders of springs and brooks; still others, especially in the western United States, inhabit dry plains, remaining dormant during the drought of summer. They are propagated readily by division if the plant is fairly large, and in some nine of the American species by runners. Sometimes seeds are used, but not commonly. However, species of the northeastern United States germinate readily in April, if fresh seed is sown in autumn in boxes and exposed, covered with burlap, to the freezing cold of winter. Many species, that grow mostly to single sterns in the wild, make large clumps under favorable conditions in the garden (Fig. 3942). But few of the native violets are grown to any extent as garden plants. V. pedata, the bird's-foot violet, a most attractive species, is sometimes cultivated, as is the hardy grower, V. papilionacea (Fig. 3936). A partial albino of this, the petals white with a large blue center, is grown in southern gardens as "the confederate violet." It has been published as V. Priceana, the type coming from Bowling Green, Kentucky; but it is perfectly hardy in the North, and multiplies abundantly. Many hybrids of V. sororia and of V. pedatifida are also hardy, some with violet flowers, others with white flowers, often fifty or more blooming at once in a large clump.
No attempt is made here to describe all the native species, as they are so numerous and so rarely horticultural subjects. For any desired information regarding them the reader is referred to the most recent editions of Gray's "Manual," of Britton & Brown's "Illustrated Flora," or of Small's "Flora of the Southeastern United States," the treatment of Viola in all three works being by the present writer. However, as a matter of record, a list of those that are or have been offered in the trade is here given, and references made to illustrations found in horticultural magazines. With the recent critical studies of Viola, it is found that two or more species were sometimes comprised under a single name; it is therefore difficult, in some cases, to determine what plant may be in cultivation under one of the older names. It is now considered that the European V. canina is not indigenous in America; probably the plant listed under that name is V. conspersa.
Pests and diseases
- Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963