3) Pollen from the вате flower is sterile or impotent on the stigma.
While there is wide provision for cross-pollination among flowers, they very often retain the power of self-pollination, so that, in the event of the failure of cross-pollination, before the period of blooming closes self-pollination may occur.
The more common ways in which this is accomplished is as follows:
1) The stamens lengthen, contract, or bend so that the anthers touch, or drop pollen on the stigmas.
2) The pistils lengthen, contract, or bend so that the stigmas receive pollen from the anthers.
3) If lobed, the lobes of the stigma roll back so that they touch the anthers.
4) The filaments and styles become twisted together.
5) The corolla in wilting closes, causing the stigmas to be pollinated.
6) Self-pollination caused by the growth or movement of the petals.
7) Change in the position of the flower caused by the curving of the flower-stalk.
There are many plants in which self-pollination is a secondary result. There are also many which are regularly self-pollinated, and, consequently, self-fertilized. When the flowers expand, the anthers rest directly against the stigma, which thus necessarily receive the pollen.
Flowers according to the ways in which they are pollinated may be divided into three groups: