68 R. A. EMERSON 
were sun red and 38 were weak sun red, while of the liguleless-leaved plants 
28 were sun red and 71 were weak sun red. The ratio of non-crossovers 
to crossovers is 151:66, or 30.4 + 2.1 per cent of crossing-over. The 
percentage of crossing-over between Lg ig and the factor pair differentiating 
sun red and weak sun red, B B”, is, therefore, ee the same as the 
linkage between Lg lg and B b. 
Four backcross progenies, 8246-8249, involving sun red, contained 469 
-weak sun red and 396 dilute sun red plants. Of the normal-leaved plants 
153 were weak sun red and 261 were dilute sun red, while of the liguleless- 
leaved plants 316 were weak sun red and 135 were dilute sun red. The 
non-crossovers are to the crossovers as 577:288, or 33.5 + 1.1 per cent of 
crossing-over. Here again, therefore, the linkage between Lg lg and the 
factor pair differentiating weak sun red from dilute sun red, B” b, is 
practically the same as that between Lg lg and B b or between Lg lg and 
BeBe 
From the facts (1) that in crosses between any two of the three types 
sun red, weak sun red, and dilute sun red, the third type is not produced, 
and (2) that the linkage value between Lg lg and the factor pairs differen- 
tiating weak sun red from sun red and from dilute sun red is approxi- 
mately the same as that between Lg ly and B b, it seems evident that weak 
sun red is due to a factor BY” belonging to the triple allelomorphie series 
‘By Bz, b: 
it seems probable that this series of allelomorphs contains other members 
in addition to the three listed above, but there is at present little conclu- 
sive evidence in support of the idea. There are certainly several forms, 
commonly classed as dilute sun red, that differ considerably in the amount 
of red pigment developed, and certainly some of these differences are 
genetic. As is shown in the next section of this account, some of these 
differences, particularly with respect to silk, anther, and leaf-blade color, 
are due to the effect of the aleurone-color factors Rr. Environmental 
conditions, particularly soil fertility, influence the development of this 
pigment so greatly that the problem becomes a difficult one. There is, 
however, some evidence that at least two forms of dilute sun red are 
differentiated by a factor pair belonging to the series B, BY’, b. These 
forms differ principally in the amount of color in the fresh husks (Plate 
VI, 1 and 2), and to some extent in the sheaths, which are the plant parts 
most strikingly different in sun red, weak sun red, and dilute sun red. 
