In some cases flowers, which open under normal circumstances, remain closed owing to unfavourable circumstances, and self-pollination occurs as in a FIG.
Self-pollination is effected in very various ways.
Muller also suggested a modification of the Knight-Darwin law, which had left unexplained the numerous instances of continued successful self-pollination, and restated it on these terms: "Whenever offspring resulting from crossing comes into serious conflict with offspring resulting from selffertilization, the former is victorious.
Spontaneous self-pollination is rendered impossible in some homogamous flowers in consequence of the relative position of the anthers and stigma - this condition has been termed herkogamy.
Arrangement self-pollination is prevented and cross-pollination ensured by the visits of bees which come for the honey secreted by the glands at the base of the inner stamens.