116 R. A. Emerson 
so sharp a one, is seen in the effects of Pr pr on the anther and husk color 
of purples and dilute purples. The factors R’ and r’ on the one hand, 
both recessive with respect to plant color, and R’ and r’ on the other 
hand, both dominant for plant color, apparently always differentiate 
between colored and colorless anthers and silks in the purple-red series 
of plant colors, and, when B is absent, determine whether or not antho- 
cyanin forms in any part of the plant. The pair B b influences mainly the 
intensity of pigmentation. Thus, purple, A B Pl, is more strongly 
colored than is weak purple, A B” Pl, which in turn is more strongly 
colored than is dilute purple, A 6b Pl. The same relation holds between 
sun red, A B pl, weak sun red, A B” pl, and dilute sun red, A 6 pl. Brown 
color shows very little in ab Pl but is strongly developed in a B PI. 
A similar difference, however, exists between the slight brown of a B pl 
and the full brown of aB Pl. In the one case in which an effect of Cc 
has been noted, C acted as an intensifier of color. 
There are somewhat marked differences between the several factor 
pairs with respect to the stage of plant development at which their influence 
is expressed. Seedlings of purple, sun red, dilute purple, and dilute sun 
red normally exhibit no characteristic differences in intensity or extent 
of pigmentation. The Bb and Pl pl pairs, which differentiate these 
color types so sharply at a later stage of growth, do not, therefore, come 
into expression early. All of these types are more highly colored late 
in their growth period than they are as seedlings, but the later changes 
are much more pronounced, for instance, in dilute purple than in dilute 
sun red, and somewhat more so in purple than in sun red. Apparently, 
Pl exerts its influence comparatively late, but under the intensifying 
influence of B, even PI expresses itself fairly early. 
The several factor pairs differ more or less with respect to the particular 
plant parts affected. Differences in the expression of B, B”, and b are 
more apparent in the husks and the sheaths, particularly the upper sheaths, 
than elsewhere. When plants of the genotype a B pl, commonly classed 
as green, show any brown, the color is limited to the sheaths and the 
outer husks. The difference between purple (A B Pl) and sun red (A B pl) 
on the one hand, and dilute purple (A b Pl) and dilute sun red (A b pl) 
on the other, is more pronounced in the husks and the sheaths than 
elsewhere. Little difference is apparent between the two groups with 
respect to the color of anthers, glumes, silks, and the like. The pair 
