The Cytoplasm as Specific Substrate 197 



an important, well-established, and basic insight into the hereditary 

 process by calling completely diflFerent things, with only one feature 

 in common, by the same term, the meaning of which is diluted and 

 made vague. Self-duplicating cell organelles, parasites and symbionts, 

 intermediates between cell structures and symbionts, as which we 

 coiild describe plastids and probably mitochondria, all become genes. 

 Why not simply speak of self-duplicating cytoplasmic elements of 

 different types, and avoid the danger of advancing unproved theories 

 of the gene as the basic element of the living world by a suggestive 

 terminology? ( We shall return to this at the end of the chapter. ) 



THE CYTOPLASM AS 

 SPECIFIC SUBSTRATE 



A. MATERNAL INHERITANCE AND CONDITIONING 

 OF THE CYTOPLASM 



At first sight Toyama's "maternal inheritance" does not seem to 

 have anything to do with cytoplasmic heredity, for maternal inherit- 

 ance is simply Mendelian heredity of a character determined in the 

 egg before fertilization. As a result, an apparent Fi is actually the P 

 generation with the maternal character, while F2 in the experiment is 

 actually Fi for the egg character, and so on. This fact, by the way, is 

 sometimes much confused by saying that in this case there is a lag 

 of a whole generation in the action of a gene ( e.g., in Darlington and 

 Mather's textbook, 1949). A "gene" can of course not act upon a 

 character of a grown egg cell before this cell is there. To return to 

 the facts: for a trait like the pigmentation of the serosa of the egg 

 (in the silkworm) as studied originally by Toyama and Tanaka and 

 recently by Kikkawa ( see 1953 ) , the foregoing characterization covers 

 the entire story, though interesting complications may arise which are 



