The Cytoplasm as Specific Substrate 217 



relation to the predetermining effect of Y in the future male-deter- 

 mined egg, and shall return to the subject later.) 



Oehlkers ( 1938 ff. ) analyzed species crosses of the plant Strepto- 

 carpus in which pure plasmatic inheritance of sex-determining actions 

 seems to be established. He crossed six different species of Strepto- 

 carpus (Gramineae) and found that they fell into two groups. Crosses 

 within the groups do not show the plasmatic effect, but those be- 

 tween the groups do. In reciprocal crosses {Rexii = A; Wendlandii 

 = B ) the hybrids show the following differences. Flowers of A X B 

 are hermaphroditic like the parents, but B X A have no anthers, 

 only staminodia. In RF2 (B X A) X A half the offspring are like 

 B X A; in the other half, all anthers are replaced by female organs 

 in a series of transitions from staminodia to five complete female 

 organs. In RF2 (A X B) X A, however, a segregation occurs into nor- 

 mal hermaphrodites, which, though externally normal, are sterile and 

 may have rudimentary ovaries. Thus B cytoplasm makes for an 

 intersexual shift toward femaleness, and A cytoplasm moderately 

 toward maleness. 



Different interpretations have been proposed by Oehlkers ( 1938, 

 1940, 1941), by Hartmann (1943), and by Goldschmidt (1938^?), 

 but all require that in the cytoplasm of the pure species a con- 

 dition exists, a plasmon, which acts in the opposite direction from 

 the nuclear genome. The distribution of this plasmon among the 

 species indicates an old evolutionary diversification. (See the remark 

 on cytoplasm and evolution in II 2 C c. The details of the present 

 analysis will be taken up later in the chapter on the theory of sex 

 determination. They will turn out to be more complicated than is 

 assumed here.) 



In Wettstein's early work there was a tendency to assume the 

 existence of genuine plasmon heredity. However, it seems that only 

 one trait in his mosses, the length of the midvein of the moss leaf, 

 remained purely maternal. All other traits influenced by the cyto- 

 plasm were matroclinous and therefore fell into the category of cyto- 

 plasm-influenced genie action. Later Wettstein (1946) thought he 

 had found a case of genuine plasmon action in Linum, in which 

 plasma-dependent pollen sterility had already been described by 

 the Bateson school (see II 2 C b). Wettstein made long-continued 

 backcrosses which resulted in completely homozygous genomes of 

 the race "tall" in the cytoplasm of "procumbents." After the eighth 

 generation the homozygosity was made still more certain by using 



