420 Action of the Genetic Material 



development is little known, though we found it at work in abnormal 

 development. It is quite possible that the position of a cell or a group 

 of cells in the whole necessarily causes (without involving special 

 genie interference) definite features of orientation, planes of division, 

 and direction of growth, which are integral for normal development 

 without being under specific genie control. There is much reason to 

 assume that such regulatory processes take place also in normal 

 development, based upon a primary property of cells, thus far little 

 understood, which exhibits itself beautifully in isolation experiments 

 ( Holtf reter ) . This would be another way of "alleviating the burden 

 of the genie material." 



Taking this for granted, genie control of pattern formation re- 

 quires the interlocking of a basic group of processes with superimposed 

 secondary and tertiary ones. The most important of these is, as 

 embryologists have discussed since the days of His, chemodifferenti- 

 ation or stratification. Whatever individual opinion one prefers — cyto- 

 plasmic stratification as a colloidal or diffusion phenomenon, or as a 

 sorting out of plasmosomes or plasmagenes, or as an orderly sequence 

 of mutation of plasmagenes, or any of the other theories discussed in 

 former chapters — one cannot explain genically controlled pattern 

 formation without localized chemodifferentiation of the cytoplasm, 

 to which I gave a general term, "cytoplasmic stratification." This 

 applies to primary and major differentiation of embryonic regions as 

 well as to such detailed peripheral patterning as the formation of wing 

 scales in a butterfly or moth. It is unknown how genie action produces 

 such stratification. One model would be the crystal in a colloidal 

 solution which initiates the Liesegang phenomenon. Another model 

 would be the setting of a gradient, for gradients certainly play a great 

 role in stratification. But how does genie action initiate a gradient? A 

 more qualitative idea would be that the genie material produces what 

 is probably a replica or partial replica of itself which, when moved 

 into the cytoplasm, catalyzes the synthesis of specific enzyme systems 

 (Spiegelman and others). But why are these sorted out in an orderly 

 spatial arrangement in the cytoplasm? Again the process of strati- 

 fication becomes more important than the biochemical nature of the 

 products of genie action, the latter of which comes into play only at 

 the next level of pattern formation. I consider this a very important 

 point in view of the great appeal of biochemical and pseudobio- 

 chemical interpretations. 



The next important genically controlled process is the timing of 

 determinative steps. Differentiation during development consists of an 



