318 Action of the Genetic Material 



with the genie material controlUng the diversification in the field (also 

 within a single cell) by producing stratification as an automatic 

 consequence of the conditions of the system. The next consequence 

 of "genie activation" and its working proceeds by means of rate 

 processes. For the geneticist this remains the primary problem, to 

 which the modern concepts, whether plasmagenes or "molecular 

 ecology," have, I fear, made very little contribution. 



The type of penetrating analysis of development and growth just 

 reported leaves the geneticist where he was, specifically where I was 

 in my book of 1927: development consists of a series of hierarchical 

 subdi\'isions of the embryonic material in regard to its intimate 

 chemistry, a subdivision or stratification which is the consequence of 

 the physical and chemical properties of the whole system and its sub- 

 systems. The stratification, an automatic outcome of the genically 

 controlled syntheses of different substances and the direction, order, 

 and place of the genically produced prompters of stratifications, 

 provides the competent material for more and more restricted genie 

 action, otherwise called the activation of the genes, which works 

 mainly by influencing rate processes. Only then do the secondary 

 effects under genie control by means of specific enzymes, hormones, 

 and auxins, and also through contacts, set in. It does not help much 

 if we express any or all of these steps in terms of plasmagenes, 

 macromolecules, and templates. In view of our ignorance about what 

 really happens, the old-fashioned general description is still adequate. 

 This, however, does not mean that, within that frame, more specific 

 notions cannot be developed. We are all anxious to see that done. 



Another embryologist, working more nearly to and beyond the 

 borderline of genetics, has repeatedly discussed our present problem. 

 Waddington (1948, 1950) starts from the fact that development is 

 essentially a sequence of chemical changes which, secondarily, are 

 also responsible for the many physical changes like surface tension or 

 permeability. These occur in the cytoplasm of the cell and certainly 

 involve different substances. The differences arise gradually and pro- 

 gressively, not as the simple unfolding of a unified trend but as a 

 series of successive steps. When two groups of cells become different, 

 not much is visible in the beginning. Their determination to different 

 developmental fates must first involve only slight chemical differ- 

 entials, but once a particular course has been set it is carried along 

 under its own steam. Each progressively increasing differentiation 

 follows a definite pattern leading to a different end result. Thus 

 differentiation is canalized into distinct pathways, and the progressive 



