322 Action of the Genetic Material 



compared with the embryological concept of competence to react 

 upon induction stimuh. (We previously used Waddington's term 

 "competence" also for the attunement of cytoplasmic substrate to 

 genie action.) These periods of competence in the present sense seem 

 to be related to the sensitive periods for genie and phenocopic action, 

 which themselves are controlled genically in regard to time and 

 duration ( Goldschmidt, 1935a). In Caspari's case it seems that the 

 competence for forming pigment has to do with the appearance of 

 RNA containing precursor granules. Caspari concludes that genie 

 action is always present in all cells so far as it produces a primary 

 genie product. An organ will react or not to this substance, if it does 

 or does not undergo a period of competence for this reaction, periods 

 which are to be understood as specific biochemical and physiological 

 states of the cell, themselves genically controlled. It is easy to apply 

 these conclusions to the primary differentiating genie actions in 

 development, our processes of stratification and gene activation. Actu- 

 ally, they are a somewhat modernized restatement of the views which 

 I have held for a long time (Goldschmidt, 1927, 1938a). 



The alternative, differentiation by genie inhibition, or inactivation, 

 perhaps occurs rarely, though there is no convincing proof for it. 



The same problem has been attacked in a somewhat different way 

 by Sewall Wright (1941, 1945a,b). After dismissing the idea that 

 differentiation is based upon intranuclear changes, he mentions only 

 briefly the possibility that certain genes are transmitted in an inacti- 

 vated condition and that irreversible activation is induced systemati- 

 cally under special local conditions. It is not clear whether this possi- 

 bility is meant to include everything we discussed thus far as "gene 

 activation," gene-controlled stratification, competence of the substra- 

 tum for genie action. Since these theories are neither mentioned nor 

 discussed by Wright, it seems that they are included. But some of the 

 following statements may also be changed into terms of our previous 

 discussion. In one place Wright states that the usual and most probable 

 view is that cellular differentiation is cytoplasmic and must therefore 

 be transmitted to daughter cells by cytoplasmic heredity. An objection 

 to this, according to Wright, is that the germ-line cells do not show 

 differences between daughter cells. A solution for this difficulty might 

 be that evolution has produced a line of cells (the germ track) with 

 plasmagenes lacking in prosthetic groups and hence in specialized 

 activity. The same plasmagenes in somatic cells are capable of com- 

 bining with such groups emanating from the nucleus, to form mole- 

 cules that multiply thereafter as plasmagenes of a more specialized 



