Genie Control of Development 309 



be used for the synthesis of coenzymes containing adenylic acid. In 

 all these deliberations, the DNA is more or less omitted. 



Thus Brachet considers genetically controlled difiFerentiation to 

 consist of the synthesis of the specific proteins which give rise to 

 histological differentiation under the action of the microsomes and 

 their RNA, which are distributed along well-defined gradients. He 

 directly calls these particles plasmagenes. "One can imagine that the 

 fertilized egg contains an enormous population of particles differing 

 one from another, and that, as a result of competition taking place in 

 the different regions of the heterogeneous egg, certain types will 

 become established in a definite territory of the embryo." However, 

 he also mentions the possibility that the differentiation could be the 

 result of the attainment of a threshold in the concentration of certain 

 substances (an idea which plays a considerable role in my physio- 

 logical theory of heredity; Goldschmidt, 1927). These substances 

 might be identical with the RNA protein granules. But we are not told 

 how the differences of the regions of the heterogeneous egg are 

 produced. They are certainly controlled genically, and this means 

 before the sorting out of the microsomes takes place. Now which 

 determines which? We shall consider this problem further, on the 

 basis of Brachet's brilliant work, leaving out the unfortunate intro- 

 duction of "plasmagenes," a concept which can only simulate an 

 understanding, as we emphasized repeatedly before. 



In the introduction to the group of facts just reviewed we have 

 pointed out the difficulties encountered when conclusions relating to 

 genie actions are to be drawn from biochemical data concerning the 

 presence and behavior of a few substances. If we take the work on 

 RNA, it is hard to beheve that the manifold specificities of genie 

 action could be exercised by a non-orderly synthesis and expulsion 

 from the nucleus of one substance, RNA. Assuming that there are 

 thousands of different DNA protein types making up the genie 

 material, what sense would the orderly structure of the chromosomes 

 make if their different genie products became haphazardly mixed up? 

 Of course Brachet considers a secondary sorting out. However, if this 

 is so, the production of the proper substrates in time and pattern, which 

 take care of the sorting process, would be the real genie actions. If 

 this is true, as it probably is, the microsomes and their RNA become 

 only a chemical apparatus of which the real genically controlled 

 processes (based upon the proteinic moiety of the chromosomes) 

 make use. We refer here to our former discussion of the manifold ways 

 in which DNA can be taken into the growing oocyte from outside, 



