The Problem of Adaptation 



ii 



" As soon as this has taken place the anthers, which have 

 been closed hitherto, dehisc and become freely accessible," 

 as a result in the change in the stigma and of the collapse 

 of the hairs at the base of the enlargement which has 

 widened. The fly can now crawl under the anthers, and, 



Fig. I. — The fertilization of Aristolochia Clematitis. A, portion of stem with 

 flowers in axil of leaf in different stages. B, longitudinal sections of two 

 flowers, before and after fertilization. (After Sachs.) 



if it does so, new pollen may stick to its back. At this 

 time the hairs in the throat dry up, and the fly can leave 

 its prison house, Figure I C. If the fly now enters another 

 flower this is fertilized by repeating the process. The unfer- 

 tilized flowers stand erect with widely open mouths. As soon 

 as they have been fertilized they bend down, as seen in 



