270 PHYSIOLOGICAL GENETICS 



panschure arc attributed thus exclusively to the constant prop- 

 erties of the plastids themselves. If Renner's views prove to be 

 correct, the facts regarding plastid inheritance will be ruled out 

 of the problem of cytoplasmic action. 



('. Cytoplasmic Influence upon Gene-controlled 

 Charactkrs 



It is very significant that though no cytoplasmic influence upon 

 the action of genes in controlling visible characters has been 

 found, when simple mutants were involved in the cross — one 

 exception will be mentioned later — quite a number of cases with 

 positive results are available that are all alike in that the sys- 

 tematic distance between the parents is rather large. If we 

 omit at present the matroclinous species crosses which always 

 have been suspected of being caused by cytoplasmic differences 

 of the parents, the first properly analyzed case was found by 

 Goldschmidt (19246). The Mendelian characters in question 

 were differences between subspecies or geographic races of 

 Lymantria dispar, viz., amounts of pigmentation in the cater- 

 pillars of different races. The type of heredity found may be 

 indicated by the following diagram which applies to practically 

 all other cases. 



Range of Variation 



P, dark 



1\ %ht, 



F,. dark X light 



Fi, light X dark 



F 2 , (dark X light) 2 



F 2 , (light X dark) 2 



This means that Fi is matroclinous and that in F 2 a 1:2:1 

 segregation takes place, the range of which, however, is shifted 

 in the reciprocal F 2 toward the maternal side. A corresponding 

 effect was obtained also in backcrosses. The conclusion, then, 

 was that it is not irrelevant for the action of the genes on which 

 or within which cytoplasm they are acting. Within the two 

 races, the respective phenotype was the result of the action of 

 the genes, given the specific cytoplasm. If the same genes, 

 however, were working within a different cytoplasm, the result 

 of their action was shifted toward the type to which the cytoplasm 

 belongs. Light genes in dark cytoplasm — to use these brief 



