CYTOPLASM AND ACTIVATION OF THE GENE 271 



designations — produce also in extracted homozygous condition 

 a phenotype that is darker than the pure light race, and, vice 

 versa, dark genes in light protoplasm fail to produce the com- 

 pletely dark forms among the homozygous segregants. When 

 .the same experiments were performed with different races dis- 

 tinguished by the presence of less and less light allelomorphs 

 of the same dark gene, the same result was obtained but in a 

 lesser degree. There can be no doubt that the geographic races 

 in question were different in regard to some element of their 

 plasmatic constitution. Since that time, other quantitative, 

 gene-controlled characters in the same material were found to 

 behave exactly in the same way, e.g., length of hibernation and 

 velocity of larval development (see review in Goldschmidt, 

 19346). 



In recent years, a number of observations of a similar type of 

 inheritance have been made, and with attention drawn to this 

 problem more cases will be available. I mention only the report 

 by Murray and Little (19356) who found that hereditary tumor 

 incidence in mice, studied in reciprocal Fi and F 2 , behaves exactly 

 as the case just reported, thus showing an influence of the cyto- 

 plasmic condition. 



In this piece of work, however, one important check was 

 missing, viz., the analysis of the extracted homozygotes in further 

 generations, which could not be made for technical reasons. 

 But similar work has been done since with similar results and the 

 additional filling of the just-mentioned gap, at least in part. 

 We shall soon see, however, that a decisive point is thus far 

 not settled. Of first importance in this connection is Wett- 

 stein's (1924-1934) work with mosses. In this material, crosses 

 between races, species, genera, and even subfamilies are possible, 

 whatever this may mean among bryologists. Generally speak- 

 ing, the crosses between races of one species were reciprocally 

 alike and did not show any influence of the cytoplasm upon the 

 gene-controlled characters. All other combinations, however, 

 showed such an influence, increasing with the taxonomic distance. 

 Among the characters studied, some, like the form of leaves, 

 showed very clearly the plasmatic influence after the manner 

 that we have just discussed for the Lymantria case; others showed 

 it as less pronounced or not at all. In the case of the leaf char- 

 acter, it was possible in the species cross to obtain a further back- 



