LETTING THE BEES DO THEIR WORK 



and still perform its function. The arrangement 

 between stamens and pistil of the yucca is such 

 that no other insect is likely to poUenize it, even 

 were there other insects at hand. 



All in all, as I said, this is one of the most 

 curious and thought-provpking instances in all 

 nature of mutual dependence between an animate 

 creature and a plant. 



One can scarcely leave the yucca and its strange 

 visitor without inquiring how so extraordinary 

 a coalition could have been brought about. 

 Unfortunately no very precise answer can be 

 supplied. We can only assume that the complex 

 and intricate relationship now manifested is the 

 final result of a long series of slight adaptations 

 through which insect and plant were mutually 

 specialized in such a way as to conform to each 

 other's needs. 



It is impossible to conceive that any sudden 

 mutation of form on the part of the plant or of 

 habit on the part of the insect could have led to 

 so complicated an alliance. 



The change must have been very slow and 

 gradual. First, we may suppose a condition in 

 which the ancestors of the yucca were sometimes 

 visited by the ancestors of the moth, but were not 

 dependent on them for any very complicated 

 method of poUenation. Then successive ages in 



[201] 



