The floral biology of Viola riviniana Rchb., V. reichenhachiana Jord. and V. hirta L. is described in detail. The flowers are very complicated morphologically and many changes in the floral organs occur during anthesis. Differences in the flowering periods of the three species were found but comparisons of the length of flower life, the pollen and nectar presentation and the receptivity of the stigmatic surfaces showed few differences between species. Movements of the pedicel and corolla directly affect the outline and colour patterns presented by the flower and these are probably of prime importance in the attraction of insect visitors to these species. All the movements of the floral organs and the changes which they undergo together suggest that anthesis has two distinct phases. The first is characterized by the retention of pollen within the androecium and the second is characterized by the gradual displacement of pollen from the anthers to the petals. Pollination during the flrst phase is effected only by a few insect species which operate the pollination mechanism precisely. By contrast, pollination during the second phase may be effected by a wide variety of insect visitors and is not, therefore, entirely dependent upon the activities of a small number of highly adapted species, as previously supposed. This may be of critial importance to the many species of Viola which are predominantly in‐breeders. In the absence of highly adapted pollinators (which is frequently the case), the second phase of anthesis may be the only opportunity for out‐breeding. The frequency of pollen exchange in the three species is, therefore, partially dependent upon the change in the mode of pollen presentation during anthesis. Copyright © 1969, Wiley Blackwell. All rights reserved
