Variation and Adaptation. 151 



insuring such uniformity are almost insuperable. And 

 if tliese differences cannot be removed in our experiments 

 it is obvious that the eft'ect they have in nature must be 

 considerable. So that a sowing of dissimilar seeds in 

 nature gives more promise of a strong generation than 

 a sowing of similar seeds. For the conditions obtaining 

 in the different parts of a circumscribed area, as far as 

 they affect the germination and growth of a seed are very 

 dift'erent, partly on account of differences in dampness 

 and fertility — which varies inversely with the degree of 

 exhaustion of the soil — partly on account of enemies in 

 the shape of animals and partly on account of competitors 

 in the shape of plants between which they happen to be 

 lodged. But if the number of seeds is great and the 

 differences between them are considerable, there is every 

 likelihood that at any rate some of them will find a situa- 

 tion which suits them. 



Let us take a particular case and compare the varia- 

 bility which exists in nature with that which is exhibited 

 by a population produced by sowing the seeds of a single 

 plant. I have chosen as an example the yellow corn- 

 flower of our fields (Chrysanthemum segetum) and have 

 paid attention to the number of ray-florets on the inflor- 

 escence.-^ The average number of these is 13; but the 

 plants vary round this value in the one direction to 6, in 

 the other to 21. 



Dr. H. W. Heinsius has been kind enough to make 

 some observations for me in the field in North Brabant 

 in the Netherlands; they involved the counting of ray- 

 florets on 325 flowers. In 1894 I sowed the seeds of a 

 13-rayed plant and counted the ray-florets of the first 



^ Ueher Curvcnselection hei Chrysanthemum segetum, Berichte 

 d. d. Bot. Ges., 1899, XVII, pp. 87-89. The numbers given there are 

 here reckoned as percentages. 



