Fig. 454.
Viola cucullata; blue flowers above, cleistogamous flowers smaller and curved below. Section of pistil at right.
848. But there are many flowers in which both stamens and pistils are present, and yet in which cross pollination is accomplished through the agency of insects.
859. Pollination of the bluet.—In the pretty bluet the stamens and styles of the flowers are of different length as shown in figures [455], [456]. The stamens of the long-styled flower are at about the same level as the stigma of the short-styled flower, while the stamens of the latter are on about the same level as the stigma of the former. What does this interesting relation of the stamens and pistils in the two different flowers mean? As the butterfly thrusts its “tongue” down into the tube of the long-styled flower for the nectar, some of the pollen will be rubbed off and adhere to it. When now the butterfly visits a short-styled flower this pollen will be in the right position to be rubbed off onto the stigma of the short style. The positions of the long stamens and long style are such that a similar cross pollination will be effected.
Fig. 455.
Dichogamous flower of the bluet (Houstonia cœrulea), the long-styled form.
Fig. 456.
Dichogamous flower of bluet (Houstonia cœrulea), the short-styled form.