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THE AMEBIC AN NATURALIST [Vol. LI 



hereditary behavior. "We have thus a factor here which 

 evidently has such a relation to the other members of the 

 factor system that only under peculiar environmental con- 

 ditions does it disturb the normal course of somato- 

 genesis. Miles (1915) has likewise investigated a type of 

 chlorophyll reduction in maize in which the recessive 

 forms are yellow seedlings which usually show a dis- 

 tinct greenish tinge at the tips of the leaves. This type of 

 chlorophyll reduction displays normal Mendelian be- 

 havior in inheritance giving in the progeny of hetero- 

 zygous plants a ratio of approximately three seedlings 

 which are of the normal green coloration to one which is 

 of the yellowish type. The heterozygous plants possess 

 the normal depth of coloration and can not be distin- 

 guished from those which are homozygous for the produc- 

 tion of normal chlorophyll coloration. The yellow seed- 

 lings on the other hand form a distinct and easily recog- 

 nizable class with no tendency toward intergradation, an 

 observation which we have ourselves been able to con- 

 firm in independent mutations involving this locus. Usu- 

 ally these seedlings die as soon as the food material in the 

 endosperm is exhausted, for under ordinary conditions 

 the change in the locus is incompatible with a normal de- 

 velopment of the individual, it is too profound an altera- 

 tion to give a normally functioning factorial system. 

 Miles found, however, that when the yellow seedlings 

 were grown under particularly favorable conditions, they 

 developed a normal chlorophyll coloration and produced 

 plants which were able to go on through the cycle of 

 changes included in the normal development of the maize 

 plant. Now this behavior can not be referred to any 

 change of the reduction locus back to the original condi- 

 tion, for the progeny of such plants consisted entirely of 

 yellow seedlings; indeed, such a reversion would be incon- 

 ceivable. Obviously the explanation of the situation will 

 be found only through a consideration of the system with 

 the recessive reduction locus. Normally this unchanged 

 locus performs a definite function in determining the pro- 

 duction of chlorophyll in the plant, but this function is 



