8 DARWINISM STATED BY DARWIN HIMSELF. 



But it may be said, granting that changed conditions 

 act on the sexual elements, How can two or more plants 

 growing close together, either in their native country or 

 in a garden, be differently acted on, inasmuch as they 

 appear to be exposed to exactly the same conditions ? 



EXPERIMENTS IN CROSSING. 



p cr wj I n m y experiments with Digitalis pur- 



purea, some flowers on a wild plant were self- 

 fertilized, and others were crossed with pollen from 

 another plant growing within two or three feet distance. 

 The crossed and self -fertilized plants raised from the 

 seeds thus obtained produced flower-stems in number as 

 100 to 47, and in average height as 100 to 70. Therefore, 

 the cross between these two plants was highly beneficial ; 

 but how could their sexual elements have been differen- 

 tiated by exposure to different conditions ? If the progeni- 

 tors of the two plants had lived on the same spot during 

 the last score of generations, and had never been crossed 

 with any plant beyond the distance of a few feet, in all 

 probability their offspring would have been reduced to 

 the same state as some of the plants in my experiments 

 — such as the intercrossed plants of the ninth generation 

 of Ipomcea, or the self-fertilized plants of the eighth gen- 

 eration of Mimulus, or the offspring from flowers on the 

 same plant ; and in this case a cross between the two 

 plants of Digitalis would have done no good. But seeds 

 are often widely dispersed by natural means, and one of 

 the above two plants, or one of their ancestors, may have 

 come from a distance, from a more shady or sunny, dry 

 or moist place, or from a different kind of soil containing 

 other organic seeds or inorganic matter. 



