Fertilization of Flowers. 



1*;:) 



incurved margin of the aperture. But there is a small place of exit on 

 each side at the base, just beneath the anther cells, and in creeping 

 out here it brushes against the viscid surface which causes the pollen 

 to stick to and go with the bee in its flight. 



Although the structure of most of these flowers is so clearly de- 

 signed to secure cross-fertilization, and indeed to render self-fertiliza- 

 tion impossible, in a few species the design is just as clear to reverse 

 this arrangement. But these are the exceptions which prove the rule. 

 We find them almost everywhere in nature as if to make us cautious 

 in drawing conclusions from insufficient data. 



The question might be asked, why the peculiar structure of the pollen 

 in orchids? Why should it cohere in masses and all go together? Surely 

 there must he some design in such a strange departure from the gen- 

 eral character of pollen? The answer is this: The seeds of orchids 

 are very minute and very numerous. Darwin estimated that a common 

 English species produced about 6000 seeds in one capsule. In another 

 species Muller estimated them as high as 120000 in a capsule. One 

 pollen grain being necessary for the fertilization of each ovule, it is evi- 

 dent that a vast number of pollen grains must lodge on the stigma of 

 such a plant in order to fertilize all its ovules. It is easy to see, if the 

 pollen did not cohere in masses, that it would not be likely to be 

 applied insufficient quantity to fertilize all the ovules and the ordinary 

 number of seeds would be greatly diminished. 



A more familiar but no less interesting example of singular structure 

 is afforded by the flowers of the Indian turnip, Arisoema triplnjlhtm. 

 Its unusual style of inflorescence has excited the curiosity of many 

 botanists and even of some who are not botanists. Its long tubular 

 spathe, with its indexed roof-like summit and its longitudinal stripes 

 of alternating colors, its small flowers situated almost at the bottom 

 of the tube and the long smooth club-like and apparently useless pro- 

 longation of the spadix above them,have each in turn been the objects of 

 admiration and curious wonderment. Yet each part of the flower has 

 its duty to perform and each is indicative of an intelligent design. 

 All work together for the common good of the species and aid in 

 securing cross-fertilization. The flowers are commonly dioecious, but 

 occasionally a plant occurs in which both stamens and pistils occur on 

 its spadix. In this case the stamens are just above the pistils and 

 both are near the base of the spadix. In the dioecious state the pollen 

 must be* brought from a staminate to a pistillate plant. An insect 

 allured by the prospect of food settles upon the outside of the spathe. 

 Having found the entrance at the upper part of the tube the broad 



