274 PHYSIOLOGICAL GENETICS 



there is an additional set of facts derived from species crosses in 

 plants, where no Fj generation is available. Most of this work 



has been done in crosses between Epilobium species by Kenner. 

 Lehmann, Schwemmle, and Michaelis (see Michaelis, 1933-1936). 

 We shall try to isolate the decisive facts from the considerable 

 body of details, facts that, however, are more nearly related to 

 the experiments in merogony than to those discussed thus tar 

 and still complicated by the fact that one of the characters that 

 has been studied is pollen sterility. (A more detailed review and 

 discussion are found in East, 1934.) Crosses between different 

 species may be reciprocally different. If they are different. 

 certain quantitative characters are always involved, which appear 

 to be inhibited in one cross. But within one species are also 

 found different biotypes which show this reciprocally different 

 inhibition after crossing. If a hybrid is backcrossed to the 

 paternal species, and this is repeated over and over again in 

 succeeding generations, finally plants are secured that contain 

 practically only paternal chromatin within maternal cytoplasm. 

 All their species characters resemble, in fact, those of the paternal 

 species, but the inhibitory action on quantitative characters, like 

 corolla length and pollen fertility, remains constantly on the 

 maternal side, as in Fi. 



It should be added as a remarkable fact that the cytoplasmic 

 influence is stronger upon the haploid characters. Pollen fertility 

 reacts much more strongly to a foreign cytoplasm than sporo- 

 phyte characters (see Michaelis and Wertz, 1935). No doubt 

 a plasmatic influence upon gene-controlled characters is visible 

 in this case. Later, we shall mention some additional details. 



Let us try now to find out the general features of the facts just 

 reported. The following conclusions seem to be warranted: 



1. A considerable number of known cases show r that the action 

 of the genes in controlling hereditary traits is different, when the 

 same genes are working within a different cytoplasmic sub- 

 stratum. In some cases, this is known for definite genes; in 

 others, only for the whole genie outfit. 



2. The action of the cytoplasm might consist in shifting the 

 genotype toward the type of the parent that has furnished the 

 cytoplasm, i.e., the mother. It might also consist in inhibiting 

 the action of single genes or of all genes, if they are situated 

 within a definite foreign cytoplasm; this inhibition might act 



