4l8 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



the resulting plants, as described by Darwin, were more vigorous 

 than those of cross-bred origin. That they were less self-fertile 

 than cross-fertile, however, is apparently in no way connected 

 with their vigor. 



The cases of plants reported by Darwin that were feebly self- 

 fertile but strongly cross-fertile suggest quite strongly that he 

 may have been dealing with the same phenomenon of incom- 

 patibility that is frequent in the case of the self-sterility which 

 he observed in Reseda and EschschoUzia. A more extended study 

 of these plants in pedigreed cultures might have convinced Darwin 

 of this point. 



The opposite view from that of Darwin on this particular ques- 

 tion has been expressed by Burck ('08) who has very fully sum- 

 marized Darwin's results, and much available data in connection 

 with his own observations on various cleistogamous species. 

 Burck especially points out that (i) plants that are regularly 

 self-fertilized show no benefits from crossing, (2) that nowhere in 

 wild species is there evidence of an injurious effect from self- 

 fertilization, and that there is abundant evidence of continued 

 vigor and high fertility resulting from long continued self- 

 fertilization, and (3) that the advantage derived from crossing 

 within or between garden varieties appears when there is doubtful 

 purity, and Is due to the fact that both vigor and fertility have 

 already been decreased by hybridization, and that when crosses 

 do give increased vigor and fertility the cross has restored in 

 increased measure the original nuclear organization of the parent 

 species. 



Especial emphasis is given to the fact that Darwin worked with 

 so-called impure varieties and that when continued self-fertiliza- 

 tion resulted in a purer strain, as in the cases of Ipomoea and 

 Mimulus greater fertility and vigor appeared from self-fertilization 

 than resulted from cross-fertilization. Burck points out, as Dar- 

 win realized, that these facts are not in harmony with Darwin's 

 general contention regarding the Injurious effects of self-fertiliza- 

 tion. 



Burck considers that sexual affinity depends more upon simi- 

 larity than dissimilarity; the degree of fertility depends upon the 

 degree of harmony in respect to the total number of "anlagen" 

 borne in the nuclei. The facts, Burck contends, support the view 



