Cross-Fertilization of Flowers hy Insects. 251 



It appears that the problem permits of a wholly different 

 solution. Among the few writers who admit this there is, 

 perhaps, none who speaks with as much decision and who 

 adduces as many facts to prove his assertions as does Mr. Mee- 

 han. In his interesting paper entitled "Are Insects any 

 Material Aid to Plants in Fertilization ? " the conclusions are 

 as follows : — 



First, the great bulk of coloured flowering-plants are self- 

 fertilizers. 



Secondly, only to a limited extent do insects aid fertiliza- 

 tion. 



Thirdly, self-fertilizers are every way as healthy and 

 vigorous, and immensely more productive, than those depen- 

 dent on insect-aid. 



Fourthly, that where plants are so dependent they are the 

 worse fitted to engage in the struggle for life, the great under- 

 lying principle in natural selection. 



These views are directly opposed to the impression one 

 would naturally receive from text-books on botany. It is 

 evident that it is of the utmost importance to study the 

 significance, and, if possible, the cause of each of the various 

 factors with which we have to deal as pointing either towards 

 cross- or towards close-fertilization. As already suggested, 

 it is always a critical matter to generalize where thousands of 

 species are concerned which have developed under a variety 

 of circumstances. 



Let us now consider the chief adaptations which point 

 towards cross-fertiliz ition : — 



I. Distinct sexes. 

 II. Specially adapted or conspicuous corolla. 



III. Peculiar position of stamens and pistils. 



IV. Difference in the time of maturity of stamens and 



pistils. 



I. Distinct sexes. — The male and female flowers being 

 separated, it is a matter of necessity that the pollen of one 

 flower finds its way to the stigma of' another flower. From a 

 teleological point of view the intention is clearly shown. We 

 cannot, however, speak with certainty of cross-fertilization 

 even in all these cases, except in wholly dioecious plants, at 

 least not in Darwin's understanding of the term, which is 

 that " cross-fertilization always means a cross between 

 distinct plants raised from seeds." We must therefore be 

 careful not to include too hastily in this category monoecious 



