68 BULLETIN 754, U. S. DEPARTMENT OF AGRICULTURE. 
coupling over Yule’s coefficient of association, which is not affected by | 
the Mendelian proportions of the characters. 
As all our observed associations more nearly approximate the 
lower coupling series of 3-1-1-3 than any of the others proposed, the 
degree of association has been measured by Yule’s coefficient of asso- 
ciation (14), which has proved very satisfactory except in cases 
where one class is unusually low. This method has the advantage of 
being easily executed and comparatively rapid, which is no small 
item in figuring the association for hundreds of individuals, though 
its general application has been challenged by Heron (10). 
As we are primarily concerned with comparing observed correla- 
tion with theoretical expectation rather than accurately measuring 
the degree of correlation, there can be no real objection to the formula 
proposed by Yule, which has been used throughout in comparing in- 
dividuals with a common ancestry. 
GAMETIC CORRELATIONS IN THE TWO HYBRID DH 234 AND DH 237. 
In all the early crosses between the Chinese variety with waxy 
endosperm and American horny varieties the second-generation seed 
showed a correlation between the color of the aleurone and the tex- 
ture of the endosperm. The first exception occurred in the hybrid — 
Dh 234. The reciprocal hybrid Dh 237 had, however, the usual cor- 
relation between colored aleurone and horny endosperm. 
The gametic formulas for the aleurone color have already been 
considered on pages 32 and 33, where the hypothesis was adopted that: 
in the hybrid Dh 237 the gametic composition of the Chinese parent 
was cP cR and of the Algeria parent Cr cr. Adding the symbol H 
for horny endosperm texture and A for the waxy texture, we have 
for the Chinese c?/A cA and for the Algeria CRH Cri. 
In crossing cRA and CPRH a colored horny seed would result which 
when planted would make gametes CRH, CHh, cRH, and cRh, and 
when self-pollinated woutd result in ears having 3 colored seeds to 1 
white and 8 horny seeds to 1 waxy. Wherever ch and CrH are 
crossed, a colored horny seed would result, which when planted would 
make eight classes of gametes, CRH, CRh, Cr, Crh, cRH, cRh, 
erH, and crh, and when self-pollinated would result in an ear having 
9 colored seeds to 7 white and 3 horny seeds to 1 waxy. This has been 
found to be true with respect to this hybrid, with the additional fact 
that a correlation exists between endosperm texture and aleurone 
color. 
The Chinese parent of the second hybrid Dh 234 was assumed to 
have the gametic composition Crh Crh, while the gametic composi- 
tion of the Algeria parent was assumed to be CRH CRH. All the 
