228 Cytoplasm as Seat of Genetic Properties 



ultimate origin of kappa, it provides us with a model of a cytoplasmic 

 particle responsible for a specific hereditary trait. But I think it 

 dangerous to say with Ephrussi (1953) in another place — actually 

 italicized — that "the killer phenotype offers us another example of a 

 character, the development of which depends both on the cytoplasm 

 and on the nucleus." Kappa is no character; it does not depend upon 

 the cytoplasm in a genetic sense, but lives and propagates in the 

 cytoplasm if it is not prevented by a definite genetic (i.e., nuclear) 

 constitution. The non-immune cytoplasm is the natural environment 

 of the "parasite" and therefore may influence it. This is clearly no 

 genetic relationship, but one between two organisms. The kappa 

 particles have been hailed many times as the real plasmagenes. Their 

 story should make us wary of these imaginary entities. We shall return 

 to this below in a more general discussion, where Lederberg's inter- 

 pretation will be taken up. 



At this point I might add that, according to Hammerling (1946), 

 the symbiontic chlorellae of Stentor and Paramecium (real cells with 

 nucleus in this case) show most of the features of kappa particles. 

 They can be removed by differential cell division and reinfected; they 

 have a constant number, and also are genetically specific, meaning 

 specifically reacting to genetically different cytoplasm. One more 

 important point in favor of the naive interpretation is that the kappa 

 particles contain DNA, which is otherwise not present or very rarely 

 present in the cytoplasm (except in developing eggs) and thus sug- 

 gests a virus. 



It should be emphasized that the kappa particles are completely 

 different from the assumed genetic particles in yeast (mitochondria) 

 carrying the respiratory enzymes, though both types have been claimed 

 in favor of the theory of plasmagenes. The two types of bodies could 

 be homologized only through phylogenetic speculations on the origin 

 of mitochondria, which actually have been tried, but should at present 

 be treated with caution. (See further discussion below.) 



d. The plostids 



aa. Nature of plastids 



Clearly the most difficult topic in the discussion of particulate 

 cytoplasmic effects is the problem of the plastids in the plant cells. 

 The relation of these cell organelles to heredity was first studied by 

 Correns in classic experiments (see his review, 1937), and interest in 

 the topic never abated ( see Renner, 1922-1936; Rhoades' review, 1946; 



