204 Cytoplasm as Seat of Genetic Properties 



the sexual conditioning of the egg cytoplasm before fertilization by 

 nuclear determiners are relevant to the present discussion also. There 

 we have, as in the antigens in Paramecium, an alternative norm of 

 reaction of the entire cell which we can call a cytoplasmic condition 

 induced by genie control, remaining through the subsequent cell 

 generations. However, it may be shifted to the alternative by genie as 

 well as external action, as in genetic or induced intersexuality. 



Coordinating such facts and deliberations, it seems to me that 

 we must be very cautious when lining them up for a discussion of 

 cytoplasmic heredity. It is clear (assuming the correctness of Sonne- 

 born's interpretation of Dauermodifikation) that the facts demonstrate 

 one of the ways in which the genie material can control processes 

 within the cytoplasm. In a broader sense we are dealing with the 

 classic conception of genie action as a "norm of reaction" which might 

 be one-tracked or alternative or still more complicated, depending 

 upon internal (threshold) conditions or external ones controlling such 

 thresholds. The cytoplasm enters here primarily as the substrate of 

 genie action. If the facts demonstrate, as they seem to do, that environ- 

 mentally induced modifications of the genically controlled products 

 of reaction may be more or less self-perpetuating, a very important 

 insight has been gained into the ways in which the genie material 

 exercises its control of cellular (i.e., cytoplasmic) conditions; and, 

 further, how the cytoplasm is fitted to perform its genically controlled 

 duties. As a matter of fact, the possibility that cytoplasmic conditions 

 induced by the nuclear genome may become self-perpetuating is one 

 of great importance for the problem of genie action. Waddington 

 (1953a) has discussed it under the name of "epigenetic momentum," 

 and we shall meet with many facts which lend themselves to such an 

 explanation, when discussing genie action. Actually it is difficult to 

 understand genetic control of development without such a process. 

 Nevertheless, calling this a form of cytoplasmic heredity is wholly 

 mistaken, and I consider it completely misleading (though it is ad- 

 vocated by some prominent geneticists ) to use the term "plasmagenes" 

 for self-perpetuating, nucleus-induced cytoplasmic conditions. 



There is a large group of facts known in bacteria and yeast 

 which, if understood completely, would shed light on the problems of 

 Dauermodifkation. These are the facts of so-called adaptation (re- 

 views in Catcheside, 1951; Monod and Cohn, 1952). A microorganism, 

 unable to metabolize an unusual substrate, learns to do so by 

 producing the necessary adaptive enzyme, if kept for a more or less 

 long time in the new substrate. The details are variable and somewhat 



