PLASMAGENES 405 



clusively. There would be nothing surprising if experiment eventually 

 showed that, in cells which are more or less completely determined and are 

 in process of producing their final cytoplasmic constituents, the cytoplasm 

 is able to carry on synthesising these nearly independently of the 

 nucleus. However, such a fact does not yet seem to have been demon- 

 strated. Whether, if it were, we should be justified in speaking of the 

 effectiveness of plasmagenes in differentiation would be largely a matter of 

 defmition; it would depend on whether we are satisfied that such gene- 

 initiated cytoplasmic factors of limited autonomy are comparable to 

 plasmagenes of the more completely autonomous kind. 



SUGGESTED READING 



Darlington 1944, Ephrussi 1953, Haldane 1954, Chapter 7, Medawar 1947, Monod 

 1947, Sonnebom 1951a or b, Weisz 195 1. 



