Genie Control of Development 323 



sort. Differences in the local conditions may bring about a differential 

 accumulation of metabolic products arising from an interaction of 

 cytoplasm with nuclear products and the environment, and eventually 

 lead to the accumulation of new plasmagenes in particular regions of 

 the organism. Each step in the regional differentiation of cytoplasmic 

 heredity increases the diversity of local environments and so facilitates 

 further differentiation. 



Let us consider the essentials of this theory, as compared with 

 the main features of the former discussion, forgetting about the use of 

 the objectionable words "cytoplasmic heredity" and "plasmagenes," 

 both assumed to be changing during differentiation! The main points 

 to be explained are the diversification of the cytoplasmic substrate in 

 the hierarchical series of determinative steps and the fact that specific 

 genie actions are started, or raised above an effective threshold, within 

 these separated regions. The separation (our stratification) is known 

 to be genically controlled or influenced by the setting of what we 

 called the conditions of the system. In Wright's theory the cytoplasmic 

 diversity is not a chemodifferentiation, a sorting out of "molecular 

 populations," in Weiss' terminology, based upon the physicochemical 

 system of the cell and cell group, but the presence of seff-perpetuating 

 plasmagenes and the creation of new plasmagenes in the interaction of 

 cytoplasmic environment, nucleus, and plasmagenes. Thus the "condi- 

 tions of the system" are brought in, not as substrate conditions for a 

 sorting-out, stratifying process but as a help in the formation of new 

 plasmagenes. There is no activation of genie action by supplying the 

 proper substrate for it, but the relation of genie substance and cyto- 

 plasmic processes, unavoidable for any theory, is established by the 

 prosthetic groups which are supplied to the plasmagenes. Thus, it 

 seems, the processes to be explained are simply transferred to the 

 hypothetical plasmagenes. I cannot help thinking that this does not 

 aid the understanding and simply shifts one unknown to another, and, 

 in addition, credits plasmagenes with all the accoutrements of a 

 dens ex machina. 



However, it is only fair to say that Wright ( 1945 ) is awdre of 

 these objections. In a later discussion of the same subject, he states 

 that persistence (in the sense of embryonic determination) may be 

 based on interactions among constituents which make the cell in each 

 of its states of differentiation a self-regulatory system as a whole. 

 According to this view, the origin of a given differentiated state of the 

 cell is to be sought in special local conditions that favor certain chains 

 of gene-controlled reactions which cause the array of cytoplasmic 



