Fertilization of Flowers. 



165 



form a bottom to the tube. This appears to be a structure designed 

 to secure self-fertilization. What more could be asked ? There the 

 stigma is, shut up in the anther tube and surrounded on all sides by an 

 abundance of pollen. What hinders self-fertilization? When the 

 pollen is mature the tuft of hairs at the apex of the anther tube be- 

 comes deflexed leaving the aperture open and allowing the pollen to 

 escape. If now a bee settles on the lower lip of the corolla and crowds 

 its head into the throat to get at the nectar, the upper part of its head 

 or its back brushes against the deflexed tuft of hairs and jars down 

 some of the pollen which lodges on its body. About this time the 

 pistil elongates, pushes <mt the pollen and emerges from the apex of 

 the tube. It is now seen to be two lobed and these lobes, are closely 

 pressed together, being receptive only on the inner surfaces. They 

 therefore have not yet been able to receive any pollen. But now they 

 begin to separate and the terminal part of the style curves downward 

 and soon the stigmatic surfaces are exposed in just the right position 

 to brush the pollen from the back of a visiting insect. We see in this 

 example how admirably all these structures are adapted to work to- 

 gether to bring about cross-fertilization and how necessary it is to ex- 

 amine the whole arrangement carefully in order to interpret the design 



There are some plants which bear dissimilar flowers. In the " blad- 

 der campion," Silene inflata, some individuals have flowers whose pis- 

 tils are longer than the stamens; others have flowers with stamens 

 longer than the pistils. An inexperienced botanist finding one of the 

 latter kind of plants would' be likely to think that he had an example 

 of a flower designed for self-fertilization. The pollen would so easily 

 and naturally fall from the anthers above to the stigmas below. 



To what other conclusion could he come. But suppose he next finds 

 a plant of this same species with flowers whose stamens are shorter 

 than the pistils. Certainly in this case the pollen is not likely to fall 

 upward from the anthers below to the pistils above. Here must be a 

 contrivance for cross-fertilization, and it throws a doubt on his former 

 interpretation, unless he concludes that the plant is capable of both 

 kinds of fertilization. Investigation has shown that the pollen in the 

 two kinds of flowers differs. That of the short stamens does not 

 readily germinate on its associated long pistils, nor does that of the 

 long stamens germinate on the stigmas of the short pistils. Each 

 must be transferred to pistils corresponding in length to its own 

 stamens. Hence the conclusion is inevitable that this again is a con- 

 trivance designed to secure cross-fertilization. If perchance fertili- 

 zation does take place between these organs of disproportionate 



