482 GENETICS: F. M. SURFACE 
TABLE 2 
Relation of the Pubescence on the Back or the Lower Grain to the Color of 
THE Grain 
Black 
Non-Black 
PUBESCENT 
SMOOTH 
PUBESCENT 
SMOOTH 
Observed Number 
345 
2 
0 
118 
pubescence could be found. No plants with pubescent non-black grains 
have been found in this cross. However, in certain other crosses in 
which this same wild was used, a few non-black pubescent plants have 
been found. 
While the present data are hardly sufficient to prove the point, it 
seems very probable that we have here a case of partial linkage. Although 
a straight F2 generation is not the best kind of data with which to study 
linkage, certain points can nevertheless be made out. 
As the observed figures stand they represent a coupling series in which 
the gametic ratio (in Bateson's sense) is approximately 240 : 1. If the 
present supposition is correct we might reasonably expect that some 
non-black pubescent individuals should appear in the 465 plants. Their 
absence is probably due to a chance fluctuation. If we may assume that 
one such individual is to be expected in 465, this will make a total of 
three crossover plants and the gametic ratio would be approximately 
150: 1. This means that instead of appearing in equal numbers the 
different classes of gametes will be formed in the ratio 150 black, pubes- 
cent: 1 black, non-pubescent: 1 non-black, pubescent: 150 non-black, 
non-pubescent. 
In regard to the gene for pubescence on the back of the upper grains 
it will be remembered that the absence of pubescence in this case is 
dominant over its presence. In the F2 generation there are 378 plants 
without pubescence (smooth) to 87 which are pubescent on the upper 
grain. The ratio here is not 3 to 1, but 4 to 1. Likewise the relation 
between this gene and the gene for pubescence on the back of the lower 
grain gives a 9:3:4 ratio. No individuals occur which are smooth 
on the lower grain and pubescent on the upper. Apparently the gene 
for pubescence on the lower grain acts as a basic pubescence factor in a 
manner quite similar to the color factor (C) in mice, rabbits, sweet peas 
and many other organisms. In the absence of the factor for pubescence 
on the lower grain the factor for pubescence on the upper grain remains 
inactive. 
The fact that this basic pubescence factor is linked with the black 
color factor disturbs the phenotypic ratio of the non-black plants when 
