60 R. A. EMeRSonN 
Evidently, purples are differentiated from browns by the Aa pair alone, 
just as dilute sun reds are differentiated from greens. This is quite 
in keeping with the assumed genotypes, A B Pl and a BPI, for purple 
and brown, respectively. 
Two of the progenies recorded in group 3 of table 8 (page 126) involved 
both aleurone and plant color. The heterozygous parents were back- 
crossed with green A testers and produced 125 colored and 127 colorless 
seeds. The factor pair differentiating these two seed classes was therefore 
Aa. The colored seeds, A C R, produced 15 purple and 14 sun red plants, 
while the colorless seeds, a C R, gave 9 brown and 14 green plants. Since 
it is shown in the preceding paragraph that purples and browns differ 
with respect to the pair Aaalone, it may be inferred that the sun reds 
and the greens of these lots also differed with respect to Aa alone. The 
assumption heretofore made with respect to the genotypes of these color 
classes, A B Pl, AB pl, a BPl, and aB pl, for purple, sun red, brown, 
and green, respectively, is given support by this relation of aleurone 
color to plant color. 
Two of the progenies recorded in group 1 of table 9 (page 127); and one 
in group 4 of table 8 (page 126), were grown from self-pollinated plants 
known to be Aa with respect to aleurone color and found to have 644 
colored and 228 colorless seeds. The 3:1 seed-color relation shows them 
to have been AaCCRR. The colored seeds, A C R, gave 294 purples 
and 113 dilute purples, while the colorless seeds, a C R, gave 119 browns 
and 40 greens. If purples and browns differ with respect to Aa alone, 
as they have been shown to do, presumably the dilute purples and the 
greens of these lots also differ in the same way. This is in keeping with 
the assumption that the genotypes of the color classes are A B Pl, A b Pl, 
a B Pl, and ab Pl, for purple, dilute purple, brown, and green, respectively. 
These comparisons of the relations of aleurone color to plant color have 
confirmed definitely the supposition that purples, sun reds, dilute purples, 
and dilute sun reds have the dominant factor A, and browns and greens 
the recessive factor a. The comparisons have also afforded some support 
for the assumed genetic constitution of the several color types with regard 
to Bb and Pipl. More definite evidence for the latter, however, is 
afforded by the linkage relations now to be discussed. 
Linkage of plant color with endosperm color.— It has been known since 
1912 that a linkage exists between the factor pair Pl pl and endosperm 
