THE VOICE OF THE DESERT 



82 



pollen-bearing anthers and then against a stigma which 

 will ultimately conduct the gene-bearing protoplasm of the 

 pollen down to the ovules below. But he does not deliber- 

 ately fertilize the plant and it would not affect his chances 

 of passing on the torch to his posterity if the flower were 

 not fertilized. The plant uses the insect but there is no 

 active cooperation on the insect's part. 



Consider, on the other hand, what happens in the unique 

 case of the yucca and its attendant moth. In the first place, 

 though there are many species of yuccas, only a single 

 one of them — and it does not grow in this region — ap- 

 pears to be capable of getting along without the moth upon 

 which all the rest depend. Moreover the moths, in their 

 turn, are no less completely dependent upon the yuccas 

 because their larva cannot feed upon anything except its 

 maturing seeds. But this situation, which is odd without 

 being unique, is not all. What is unique is the fact that the 

 moth goes through a series of purposeful actions which 

 have no other function except to fertilize a flower which 

 could not be fertilized in any other way. If we naively 

 interpreted its actions, we should find ourselves compelled 

 to say that it "knows what it is doing." 



The classic observation was made seventy-five years ago 

 by the remarkable Missouri entomologist, Charles V. Riley, 

 though the subject has been much studied and written 

 about since Riley himseH fully described the crucial, in- 

 credible event as he observed it on a cultivated species 

 grown in the neighborhood of St. Louis. Several different 

 insects frequent the flowers to eat the nectar or the poUen 

 but perform no service in return. Meanwhile the female of 

 the indispensable B:ioth rests quietly in the half-closed 

 blossoms. 



