452 GENERAL RESULTS. CHAP. XII. 



in the first generation, a fair supply of self-fertilised 

 seeds. 



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 ? Although this question has been already 

 considered, it deserves further consideration from 

 several points of view. In my experiments with 

 Digitalis purpurea, some flowers on a wild plant were 

 self-fertilised, and others were crossed with pollen 

 from another plant growing within two or three feet's 

 distance. The crossed and self-fertilised 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 differentiated by exposure to 

 different conditions ? If the progenitors 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 genera- 

 tion of Ipomoea, or the self-fertilised plants of the 

 eighth generation 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 or 



