32 R. A. EMERSonN 
connection with the development of brown pigment, tho when both A and 
B are present, sun red pigment is produced. The pair Pl pl is so termed 
because of its relation to purple pigment. The phenotypic formulae as- 
signed to the several classes of plant color under consideration here are 
as follows: : 
ABPI— fa, purple 
A B pl — Ila, sun red 
Ab Pl —IIla, dilute purple 
Abpl — IVa, dilute sun red 
aBPI— V, brown 
aBpl — Via) 
ab Pl — VIb} green 
abpl — Vice 
Obviously the hypothesis in accordance with which the above factorial 
assignments have been made is subject to several genetic tests. Naturally 
the first tests to suggest themselves are studies of the behavior of the 
several F. types in F; and later generations. Next in order are inter- 
crosses between the several classes. For reasons that will appear shortly, 
one of these intercrosses is here dealt with before consideration is given 
to F3 generations from the several F2 classes. 
Dilute sun red IVa x brown V 
From an examination of the factorial assignments listed above, it is 
evident that crosses of dilute sun red, A b pl, with brown, a B Pl, should 
produce purple F; plants, A B Pl. Moreover, these F; purples should be 
heterozygous for all three factors, Aa Bb Pl pl, just as was assumed for 
the original cross of purple, A B Pl, with green, ab pl. The F, and later 
behavior of this cross should also, barring linkage, be like that of the original 
cross, so that the two can most conveniently be considered together. 
Generations Fy and F>.— The F; generation of twenty-six crosses of 
dilute sun red with brown plants is given in table 4 (page 123). The dilute 
sun red parent plants were chosen from any convenient lots known to be 
homozygous with respect to A, b, and pl. The brown parent plants, on 
the other hand, were from the F, and later generations of the original 
cross of purple and green or from other crosses. It was to be expected, 
therefore, that some of the brown plants would be homozygous for both 
B and Pl, and some would be heterozygous for B, some for Pl, and some 
