466 BOTANICAL GAZETTE [june 



not present. 



Muller 



L. minor and L. arvensis, and small-flowered species of Vicia, as 

 examples of plants which had descended from those adapted by 

 their floral structure to pollination by insects. In the plant we are 

 considering, this process is epitomized. Pollination by the help of 

 insects takes place in flowers of an inflorescence which gradually 

 undergoes such changes in a single season as to preclude it. The 

 process of reduction is seen in actual working, and it may be that 

 such flowers, rather small at best, are on the way to a stage where 

 visitation by insects will cease. Yet one cannot regard the explana- 

 tion as entirely valid. By the very principle of adaptation here 

 invoked, the opposite might come true; that is, visits by insects, 

 frequently repeated and continued for a long period of time, would 

 finally produce flowers better suited to their work. Irregularity 

 of floral structure is regarded as such an adaptation, and to some 

 extent has been explained by it. A causal relation between the two 

 is traced. In Darwin's list of genera with cleistogamic flowers, 

 thirty-two of the fifty-five he gives have the flowers in their most 

 advanced stage irregular. He says that this " implies that they have 

 been especially adapted to fertilization by insects." 19 Without 

 pressing such explanations too far, it is seen in the case of the wild 

 toad-flax that provision for cross-fertilization is made in the structure 

 of flowers borne simultaneously with the cleistogamous, or at an 

 earlier date, on the same plant. In this there is insured to the species 

 the present means of invigorating its life, the primary benefit to be 

 derived from it, whether it be a waning or waxing advantage. 



Chicago 



19 Darwin*, C, Different forms of flowers 339. 



* 



