Genie Control of Development 389 



subsequent similar system, the composition reached by this second 

 system will, as we have seen, not be affected by this alteration in the 

 initial concentration of one of its components. Another gene altering 

 a rate constant in this second system will therefore have no different 

 effect whether the first mutant gene is present or not. This corresponds 

 to a case of complete 'buffering,' in the development of actual living 

 organisms, the differentiation [= composition] is in general not 

 entirely independent of the conditions outside the system." 



We presented this ingenious analysis in order to show how diffi- 

 cult it is to draw tangible and final conclusions upon the interplay of 

 genie action from such experiments. At present we do not seem to get 

 beyond very general statements about interlocking, interference, and 

 attunement of genically controlled reaction chains, preferably in- 

 volving features of their kinetics. 



Much more concrete are the results when genically controlled 

 chemical end products of genie interplay are studied. But it must be 

 realized beforehand that such studies may throw very little or no light 

 on the control of morphogenesis, though they supply models for some 

 kind of interplay of determining reactions. (I have quoted Haldane's 

 more optimistic conclusions. ) A good example is the work of Lawrence 

 and Scott-Moncrieff (1935) and Scott-Moncrieff (1936) on flower 

 pigments, especially in Dahlia. Since this pioneer work was per- 

 formed, both authors have made many new additions and corrections 

 (see Scott-Moncrieff, 1939; Lawrence and Price, 1940; Haldane's 

 excellent review of the subject, 1942). We are not interested here in 

 the special biochemistry of the subject but in the general way in 

 which genie actions collaborate in the control of biochemical diversi- 

 ties. Therefore I shall use the original work, antedating present-day 

 biochemical genetics, as an example, because it brings out the points 

 I wish to make. Subsequent corrections in the biochemical details 

 (including controversial points, on which I am not qualified to pass 

 judgment) do not alter the general picture so far as genie action is 

 concerned. Some of this is discussed in Haldane ( 1954 ) . 



Keeping to the original findings, we may consider the following 

 extract, emphasizing the features of importance to the geneticist, who 

 is not so much interested in the individual biochemical facts as in 

 their general trend. In these plants, color may be determined by a 

 number of agencies. If a single pigment is involved, this and the pH 

 of the surroundings are decisive. If more pigments are involved, there 

 are various possibilities: a combination effect, a background effect, a 

 copigment effect (meaning that one is changed in the presence of 



