3472 



VINCETOXICUM 



VIOLA 



in warm or tropical parts: they are twining or trailing 

 woody or perennial herbaceous vines, with opposite 

 cordate simple Ivs. and small greenish or purplish fls.: 

 corolla campanulate or rotate, deeply 5-cleft and the 

 parts sometimes reflexed; crown small, mostly ring-like 

 or cup-like and thereby differing from the awned crown- 

 lobes of Gonolobus (Definition of Gonolobus, p. 1356, 

 to be amended): follicles thick, pointed, muricate or 

 ribbed or both. Several species are native in the U. S. 

 from Pa. and Va. southward, but apparently they are 

 not in cult. The mosquito plant or cruel plant, some- 

 times named in this genus, is here treated as Cynan- 

 chum acuminatifolium. 



VINES: Planting, Vol. V. (Index p. 2657.) 



VIOLA (classical name). Violdcex. 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 bien- 

 nials; 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 Ivs. and 1-fld. scapes from 

 the crown of the rootstock, or stemmed with manifest 

 internodes between the Ivs., 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 (cleis- 

 togamous). (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 

 f r. ; the lower petal of the nodding fl. spurred, the other 

 4 in 2 unlike pairs, the petals in each pair symmetri- 

 cally alike; stamens short and included, the anthers 

 more or less coherent in a ring about the style, 2 of 

 them with nectar-bearing ap- 

 pendages projecting backward 

 into the spur: fr. a caps, with 

 several (up to 60) obpvate 

 seeds; caps, when ripe splitting 

 into 3 boat-shaped valves with 

 thick rigid keels; as the thin 

 sides of the valve dry and con- 

 tract 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 off- 

 spring from unlike parents, it is practicable in a genus 

 like Viola to discover what forms are proper species 



3935. Structure of the 

 flower of Viola papilio- 

 nacea. 



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 



3936. The two kinds of violet flowers, the common showy 

 flowers at the right (natural size), and the cleistogamous flower 

 at a, its immature pod at b (XM)- Viola papilionacea. 



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 off- 

 spring 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 east- 

 ern North America that is, more hybrids than there 

 are pure species. In Wilhelm Becker's systematic trea- 

 tise 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 stems 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 



