246 C. p. RHOADS 



The studies of Imai (109) and of Rhoades (no) on cytoplasmic 

 control have attracted great attention in recent years. In the develop- 

 ment of chlorophyll by maize, pure genie control was proved in 100 in- 

 stances. In two cases, however, cytoplasmic inheritance was shown to 

 exist. In this plant, a specific gene has the power to cause a modification 

 of the plastid marked by smaller size and lack of chlorophyll. The modi- 

 fied plastids have genetic continuity not affected by the constitution of 

 the genes. To quote : ". . . although induced by a nuclear factor, the ij 

 gene, the mutated plastid, like a Frankenstein monster, is no longer un- 

 der the control of its maker." 



The work of DuBuy and Woods ( 1 1 1 ) provides interesting new ma- 

 terial on cytoplasmic inheritance in plants and their reports should be 

 consulted directly. They discuss the evidence for regarding plastids as 

 analogous to mitochondria with particular reference to their content of 

 ribose nucleo-protein and to their tendency to break up unless their 

 handling is carried out with great precision. The modified plastids, as 

 the source of spontaneous variegations, are discussed and a virus 

 deemed not likely to be the cause. Of special interest are the data which 

 indicate that certain plant viruses compete with the host chromoprotein 

 for nitrogen and that both normal and abnormal (virus) enzyme sys- 

 tems can be inhibited by cyanide. Success in transplanting variegated 

 plastids with resultant self-propagating abnormalities in host plants 

 are described. The likeness between these studies and the disease in- 

 duced by the cytoplasmic material of tumor cells induced by the Rous 

 agent is dramatic. 



Most interesting of the studies concerning the inheritance of cyto- 

 plasmic factors, and perhaps the most pertinent to the cancer problem, 

 are those recently reported by Sonneborn (112). This work is so im- 

 portant that it is discussed in extenso. 



Sonneborn discovered that one race of Paramecium aurelia, when 

 placed in culture with organisms of another race, killed the latter by 

 means of a substance secreted into the culture medium. This ability to 

 kill was assigned to a gene called "killer gene" or K. The recessive allele 

 of K, which was present in the animals which were killed, was called 

 "sensitive" and designated by k. The characters K and k have been 

 shown to be inherited by simple Mendelian laws, and hence animals can 

 have the genotypes : KK, Kk, kk. It was found, however, that the 

 phenotypes, or the expression of these characters, did not necessarily 

 reflect the genotypic make-up. This was due to the elaboration into the 

 cytoplasm by X" of a substance "Kappa." Kappa is the material that 



