480 
GENETICS: F. M. SURFACE 
The grain does not shatter. The base of the upper grain on each spike- 
let is like the upper grain of the cultivated variety. The Fi grain is 
pubescent on the back of the lower grain of a spikelet but unlike the 
wild the upper grain of each spikelet is entirely free from pubescence. 
There is a tuft of hair at the sides of the base of the lower grain but 
none on the base of the upper grain. Medium strong to weak awns 
occur on the lower grain of most spikelets of the Fi plants, but there are 
never any awns on the upper grain. 
The F2 generation consisted of 465 plants. A small F3 generation 
was also grown. This consisted of short rows from 70 different F2 
plants. 
The F2 generation shows that the wild parent carries a factor for 
gray glume color as well as for black. It is also probable that the wild 
carries a gene for yellow color. The cultivated parent carries the factor 
for yellow color. These three colors segregate independently of each 
other, giving 12 black; 3 grey; 1 yellow. The numbers obtained were 
347 black; 88 grey, 30 yellow, which is a very close agreement with 
expectation. 
With regard to the base of the lower grain three types rhay be recog- 
nized: (1) the cultivated base (fig. 1); (2) the intermediate base like 
that found on the Fi grain (fig. 3) ; and (3) the wild base (fig. 2). These 
three types appear in a 1 : 2 : 1 ratio on the F2 generation. The observed 
numbers are 117 cultivated: 236 intermediate: 112 wild. The difference 
between the cultivated and wild base appears to be due to a single pair 
of genes. The heterozygous condition gives rise to the intermediate 
base. 
The gene for the base of the lower grain segregates independently 
of the several color genes. For each of the three grain colors the plants 
with cultivated, intermediate and wild bases approach the 1:2:1 ratio. 
There are, however, a number of characters which in the present 
cross are always associated with a particular type of base. In all 
there are seven pairs of characters which show this absolute correlation. 
The condition of each of these characters for the three types of bases on 
the lower grain is given in Table 1. 
The present data are not sufficiently extensive to determine whether 
these several phenotypic characters are caused by the action of a single 
pair of genes or whether they are due to several pairs of genes very 
closely linked together. Nilsson-Ehle (1911) regards this group of 
characters as due to the presence or absence of a single inhibiting factor. 
In certain other crosses not yet completely analyzed but involving this 
same strain of A. fatua some of these correlations have been broken. 
