Genie Control of Development 385 



tions proposed for individual phenomena to enter the general picture: 

 velocities of reaction chains, threshold conditions, stratification of 

 cytoplasmic differences, self-perpetuating cytoplasmic conditions, sub- 

 strates, competition for substrates, and everything else mentioned at 

 different levels of the previous discussion. From all this should emerge 

 what a rather plastic German word calls a Zusammenschau, a synopsis 

 in Greek. A very good model for two dimensions has been used by 

 Goethe, when he poetically compared the fabric of thought with the 

 production of a fabric by weaving: 



Zwar ists mit der Gedankenf abrik 



Wie mit einem Weber-Meisterstiick 



Wo ein Tritt tausend Faden regt 



Die SchifHein heriiber hiniiber schiessen 



Die Faden ungesehen fliessen, 



Ein Schlag tausend Verbindungen schlagt. 



If this dynamic picture could be extended into four dimensions, it 

 would be a perfect model for genie control of development. 



A great many of the individual processes which combine to form 

 a picture of heredity as a whole have been touched upon. But there 

 are still a number of facts which relate especially to the interplay, the 

 fabric of genically controlled processes. The present chapter will deal 

 with their analysis before attempting a general synthesis. 



a. Factorial collaboration 



Insight into the interplay of genically controlled processes in 

 development should be gained from a study of the interactions of 

 different mutant loci. Such interactions were considered in a general 

 way when we referred to the genetical background, or residual 

 heredity; when we discussed the interplay of genically controlled 

 reactions under the unfortunate term "genie balance"; when we spoke 

 in a more or less specific way of modifier systems; when we found the 

 need for independently controlled threshold conditions for the effect 

 of individual genie actions; when we discussed cytoplasmic substrates 

 and their ultimate genie control; when we mentioned special pos- 

 sibilities like competition for substrates; when we discussed specific 

 interactions like those of dominance modifiers and enhancers of pene- 

 trance; and also when discussing the influence of extra heterochro- 

 matin upon certain genie actions. The entire body of classic genetics, 

 since the early work on color in mice by Cuenot and that of the 

 Bateson group on different organisms, contains innumerable examples 

 of individual genie interactions in the form of collaborations, modi- 



