3 66 



Evolution and Adaptation 



This table shows that the fertility of the legitimate to that 

 of the illegitimate is as 100 to 33, as judged by the flowers 

 that produced capsules ; and as 100 to 46 as judged by the 

 average number of seeds per capsule. It is evident, there- 

 fore, that "it is only the pollen from the longest stamens 

 that can fully fertilize the longest pistil ; only that from the 

 mid-length stamens, the mid-length pistil ; and only that 

 from the shortest stamens, the shortest pistil." 



Darwin tries to connect this fact with the visits of insects 

 to the flowers. He says: "And now we can comprehend 

 the meaning of the almost exact correspondence in length 

 between the pistil in each form and of a set of six stamens 

 in two of the other forms ; for the stigma of each form is 

 thus rubbed against that part of the insect's body which be- 

 comes charged with the proper pollen." A further conclusion 

 that Darwin draws is "that the greater the inequality in 

 length between the pistil and the set of stamens, the pollen 

 of which is employed for its fertilization, by so much is the 

 sterility the more increased." Darwin also makes the fol- 

 lowing significant comment on the problem here involved : 

 "The correspondence in length between the pistil in each 

 form, and a set of stamens in the other two forms, is prob- 

 ably the direct result of adaptation, as it is of the highest 

 service to the species by leading to full and legitimate fer- 

 tilization." He points out, on the other hand, that the in- 

 creased sterility of the illegitimate unions, in proportion to 

 the inequality in length between the pistil and the stamens 



