No. 629] DARWIN AND HYBRIDIZATION 



547 



since animals, and hence presumably plants, profit from 

 changes in their conditions, that probably such changes 

 operate to affect the germ cells, or that in some way the 

 germ cells receive an extra stimulation on that account, 

 . which redounds to the benefit of the offspring (Ic, 2 : 155). 



Darwin appears to hold the ill effects of close fertiliza- 

 tion to be due to the fact that the sexual elements in the 

 different flowers on the same plant have not differen- 

 tiated, while in his conclusion he appears to consider the 

 benefits of cross-fertilization to be due to the individuals 

 involved in the cross having differentiated through hav- 

 ing been exposed to different conditions. 



Darwin frequently emphasizes the same view regarding 

 the differentiating effects of a new environment. 



tho.se already given, of plants which are coni])ltM('ly sclt'-^UMile in one 

 country, and when brought to another, yield cnch hi ilir liisi -viicin- 

 tion, a fair supply of self -fertilized seeds (lb. 477). nii.l nu.iin. . . . we 



iri the same llistricr scores as a fresh stock and has high t'erlilizing 

 pow(Ms. The cu.ious cases of plants which can fertilize and be fertil- 



sterih.\viili'ilu.ii- own pollen, become intelligible, if the view here pro- 



AVhen two varieties wliicli iiresent well-marked differences are crossed, 

 their descendants in the later generations differ greatly from one 



obliteration of some of these characters, and to the reappearance of 

 former ones through reversion; and so it will be, as we may feel almost 

 sure, with any slight differences in the constitution of their sexual 

 elements (lb, 449). 



"With regard to the ill effects derived from self-fertiliza- 

 tion, Darwin says : 



Whether the evil from self-fertilization goes on increasing during 

 successive generations is not as yet known, but we may infer from my 



