Viola. The sepals are prolonged backwards beyond the point of insertion (appendiculate); the corolla is polypetalous, descending imbricate, and zygomorphic, its anterior petal being larger than the others and provided with a spur (Fig. [421]). The 2 anterior of the 5 almost sessile stamens are provided with a spur-like nectary, which protrudes a considerable distance into the petaloid spur (Figs. [421], [422] n, sp). The style is club-like, and bears the stigma in a groove on the anterior side (Fig. [422] st). Herbs with rhizomes, or annuals; flowers solitary. V. odorata, canina, etc., have cleistogamic flowers which produce fruit in addition to the large, coloured (violet) flowers. The Pansy (V. tricolor) has large flowers adapted for insect-pollination, and also smaller, less conspicuous ones designed for self-pollination. The stigma, as in Fig. [422] A, st, and B, is situated on the anterior side of the stylar-head, immediately in front of the channel leading down to the spur (sp); below it is situated a valve, easily covered with pollen when the proboscis of an insect is introduced into the spur, but which closes upon its withdrawal; cross-pollination is thus secured.—The sweet-scented V. odorata is visited by the honey-bee, which insures cross-pollination, and in the absence of insect visits it effects self-fertilisation by cleistogamic flowers. The conspicuous but scentless V. tricolor, var. vulgaris, is less frequently visited by insects (humble-bees). In V. silvatica and V. canina the pollen is carried on the head or proboscis of the honey-sucking bee.—The fruits of V. odorata bury themselves slightly in the soil. In the others the fruits are raised above the ground; the 3 boat-shaped valves close together along the central line, and eject the seeds, one by one, with much violence, so that they are thrown to a great distance.
Figs. 423–425.—Viola Tricolor.
Fig. 423.—Capsule after dehiscence (nat. size).]
Fig. 424.—External view of the seed.
Fig. 425.—Seed in longitudinal section.
The Alsodeia-group has regular or almost regular flowers. Gamopetalous corollas are found in Paypayroleæ. Sauvagesieæ differs the most by its regular corolla, and 5–∞ free or united staminodes.
250 species; especially in the Tropics.—The Ionidium-species are used as ipecacuanha. A number of Viola-species are cultivated as garden plants, especially V. odorata (sweet-scented Violet) and V. tricolor, which have a large number of varieties.