THE GENETIC NATURE OF TAXONOMIC DIFFERENCES 277 



the nature of the cytoplasm. But, as we have said, the degree of impor- 

 tance of the cytoplasm is very different in different characters, and 



MeHy 



HyMe 



Fig. 125. Differences in Reciprocal Hybrids in Mosses.— The species used 

 were Funaria mediterranea and F. hygrometrica; in the hybrids the maternal parent 

 is written first, e.g. in HyMe the maternal parent was hygrometrica. Above are 

 shown the pure species (haploid gametophytes). In the next row are the capsules 

 of the pure and hybrid diploid sporophytes; note the resemblance to the maternal 

 parent. In the third row are the diploid hybrid gametophytes obtained by 

 regeneration from the sporophytes; note resemblance to mother in leaf points 

 and ribs. 



(From Wettstein.) 



Wettstein concludes that development must always be regarded as the 

 result of the interaction between the genes and the cytoplasm. 



The nature of the cytoplasmic factors is obscure^; we can point to no 

 ^ Cf. Correns 1937, Renner 1934, Imai 1937. 



