Genie Control of Development 317 



is not dependent upon genie control. Growth as multiplication of cell 

 substance is the unspecific feature, but its speed, time, and place are 

 under genetic control, as innumerable facts of genetics prove. How- 

 ever, when we think of the genetics of differentiation, the concept of 

 Weiss is linked to the previous independent differentiation of his 

 template molecules in different cell descendencies (i.e., in our 

 language, to the stratification already having taken place). Thus the 

 concept of Weiss, so useful for following the stages of cellular dif- 

 ferentiation, still does not answer the question of primary differences 

 of determination, the production of the differently competent sub- 

 strates for genie action. 



Weiss himself realizes this, though, as it seems, not for the 

 primary divergences between two daughter cells but for the latter 

 configurations of the embryonic patterns in determination fields. (In 

 our opinion there is no difference between the two processes except 

 the status in the hierarchic sequences of more and more specific 

 determinations, i.e., Waddington's canalization of development.) Weiss 

 emphasizes that we know very little about this. But, he says, "it has 

 become ever clearer that growth, as such, is a purely scalar process, 

 producing simply more protoplasmic mass, increments without in- 

 trinsic direction. Direction is given to the growing mass not by 

 properties inherent in the chemical mechanism of reproduction itself 

 but by physical properties of the space into which the material issues 

 forth. Physical factors of given polarity, such as tensions, pressures, 

 electric gradients, diffusion currents, fibrous pathways and the like, 

 appear among the factors that guide . . . the growing materials . . ." 

 (i.e., what we formerly called the conditions of the system). 



The basic problem to the geneticist is finally touched in Weiss' 

 analysis when he speaks of the most difficult and most neglected of all 

 basic fields of morphogenesis, that of supercellular integration. The 

 basic fact is the existence of patterned field activities in the deter- 

 mination of embryonic events. He states, correctly, that "after all, one 

 has to explain that a determinative field vector causes not just a 

 quantitative change in the activity of a responding cell, but selectively 

 activates in the latter a specific performance from among a whole 

 series of equally possible ones, perhaps by specific molecular segre- 

 gations. This, it would seem, makes it imperative to concede to the 

 field vectors the property of affecting molecular configuration and 

 constellation, rather than only concentrations and reaction rates . . ." 

 I may add that this is just the situation throughout the entire hierarchy 

 of embryonic determinations (which I developed in detail in 1927), 



