PRACTICAL POLLINATION 257 



among the existing plants have adopted a com- 

 promise in which cross-fertilization is the rule, 

 yet which makes possible self-fertilization in 

 case, under the stress of circumstances, cross- 

 fertilization should fail to take place. 



Doubtless, on the whole, this was the best 

 course of all. The plants that adopted it might 

 be said to be the wisest of their kind. 



THE TYPICAL FLOWER 



What may be regarded as the typical or per- 

 fect flower, then, is one that contains both pollen- 

 bearing and pollen-receiving parts, surrounded 

 by the conspicuous insect signal that we term the 

 corolla; and having also a less conspicuous outer 

 shield termed a calyx. 



The calyx is the original shield about the 

 flower bud, and its function is over when the 

 flower opens. 



The botanist ordinarily speaks of the calyx as 

 modified leaves. He refers to the petals of the 

 corolla as being also modified leaves or enlarged 

 and beautified modifications of the calyx. 

 He thinks of the stamens and the pistil as 

 modified petals; and he justifies this estimate 

 by showing that under cultivation it is often 

 possible to transform these essential organs into 

 petals. 



Vol. 2 Bur. I 



