!H PHYSIOLOGICAL GENETICS 



3. The content of katalase in the white mutants is reduced to 

 about one-third the normal amount. In the cotyledon, it is still 

 normal. 



4. In two of the albino lines bill not in the others, also not in 

 colored lines, a methylated Indolyl base was found, indicating 

 specific chemical activities. 



5. In albino forms, the plastids are defective; less so in the 

 xantha. This points to the possibility that the primary effect 

 of the mutant gene is upon the plastids. In this case, the gene 

 would not be concerned directly with chlorophyll synthesis, and 

 the facts would not help much lo understand the chemical side 

 of gene activity. 



Before reporting upon the best analyzed case, flower color, we 

 shall mention a piece of work that is of a more physiological than 

 strictly chemical type, Brink's (1929a, b) studies on the waxy gene 

 of maize. This recessive gene produces among other effects the 

 presence of a specific type of reserve starch in the male gameto- 

 phyte, the pollen grain. As this gene segregates in the pollen 

 tetrad, the chain of reaction between the gene and its effect is no 

 longer than the time of the reduction division. Chemically the 

 two starches are very much alike as far as the basic sugar is con- 

 cerned, but Brink found that certain differences in reactibility 

 pointed to a structural difference. This seems to have to do 

 with the amylase, as extracts from waxy pollen give a lower 

 curve for glucose production than extracts from normal grains, 

 i.e., show a higher diastatic activity. Brink concludes from this 

 that the amylases in both cases may be different in kind and 

 therefore attributes to the mutant waxy gene the ability to 

 produce a somewhat different diastatic enzyme. 



It is not necessary here to go deeply into the chemistry of 

 flower colors. Only such facts will be mentioned as seem to be 

 important from the standpoint of gene action. We shall follow 

 mainly the most recent w r ork in the field by Miss Scott-Moncrieff 

 (1936). Flower color may be determined by a number of 

 agencies. If one pigment is involved, the color depends upon the 

 pigment in question and also frequently upon the pH of the 

 milieu. If more than one pigment is involved, different possi- 

 bilities are given as follows: 



1. There might be a combination effect. 



