THE FRAGRAXT CALLA 17 



discriminative selection on the part of insects that 

 the calla lost its scent in the past ages. For of 

 course natural selection can operate even more 

 effectively in weeding out organisms that have 

 undesirable traits as in perpetuating organisms 

 that show favorable variations. 



One process is necessarily complementary 

 to the other; they are two sides of the same 

 shield. 



In another connection we shall have occasion 

 to deal more at length with the processes of 

 natural selection; and we shall see numberless 

 examples before we are through of the way in 

 which artificial selection is instrumental in de- 

 veloping new races of plants. 



FOUNDATIONS OF NATURAL SELECTION 



But for the moment I will consider a little 

 more at length the question of the origin of the 

 variation which resulted in giving this particular 

 calla a perfume that was not normal to its race. 

 In so doing, we shall gain a clue to the genesis of 

 other types of variation or mutation through 

 which various and sundry new races of cultivated 

 plants have originated, and through which also, 

 we have every reason to believe, numberless spe- 

 cies of animals and plants in a state of nature have 

 been evolved. 



