THE CYTOPLASM 



die. A few (too few to show in the diagram, Fig. 41) even contain 

 plastids of both kinds and produce plants which are variegated 

 already as seedlings. Evidently a white plastid never changes back 

 to green. 

 The same proportions of white and variegated seedlings occur in 



GG 



CC 



p 



F 





Fig. 41. — The inheritance of variegation in barley, Hordeum vulgare, according to 

 Imai (1928). Black circles arc green plants, white circles white plants, and hatched 

 circles variegated. Size of circle indicates frequency of the type amongst seedlings. 

 Superimposed on mendelian segregation is the purely maternal inheritance of 

 irrevocably white plastids in a small proportion of the progeny of mutating 

 (variegated) plants whether selfed or crossed (after Darlington, 1944). 



the cross with pollen of a normal green barley as in the self of the 

 variegated plant. The remaining plants from this cross, however, 

 stay purely green instead of developing variegation at a later stage. 

 Plastid mutation has been suppressed. The suppressor must be a 

 dominant nuclear gene, because in the Fg a quarter of the plants are 

 variegated like their grandparent. Mutation begins again with the 



172 



