1920] COULTER— A LEU RONE COLOR 413 



color; (2) they are grains, properly colorless, in which there is some 

 partial substitute for the R or C (probably the latter, referred to 

 later) factors or both; (3) they represent something entirely 

 unrelated to the set of factors under discussion. That the second 

 is a likely explanation is suggested by three facts. 



1. The count of the original parent ear showed a marked defi- 

 ciency of colorless grains. The faint red and faint purple grains 

 had, in that count, been classified as colored. If they were truly 

 colorless grains the original ear would have very closely approxi- 

 mated the predicted 9 : 9 : 14 ratio. 



2. The nature of the original cross was such that every grain 

 must be Pp or pp, but never PP. Inbreeding, therefore, might 

 give ears with some red and no purple grains, but could never give 

 ears with some purple and no red grains. Actually that is what 

 occurred. This is, of course, merely negative evidence. Positive 

 confirmation, however, comes from a similar experiment conducted 

 with slightly different material. An ear produced by PpRrCc 

 selfed, which gave an ideal 27:9:28 ratio, was used as the basis of 

 an experiment similar to the preceding. The general results were 

 about the same and need not be discussed in full. Among the 

 purple grains, however, several produced ears which showed purple 

 and colorless, but no red grains, and one produced a full ear of 

 purple grains alone. This is to be expected from the fact that 

 genotypes including PP, although not present in the previous ear, 

 are present here. Such being the case, the behavior of the faint 

 purple grains from this ear should prove significant. From that 

 class came the following four ears: 



Light purple Faint purple Faint red Colorless 



o Some Some Many 



Some Some Many 



o Some o Many 



1 34 



4 



These certainly suggest the presence of PP in the last two cases, 

 while Pp may be inferred for all the others. It is very likely that 

 the last ear represents the homozygous condition for faint purple, 

 whatever that may be, the color being present but indistinguishable 

 in 4 grains. 



