30 
BULLETIN 146&, IT. S. DEPARTMENT OF AGRICULTURE 
Although this assumption would account for the long-observed 
deficiency of waxy seeds in heterozygous material provided the pol- 
linations were made early, the actual facts with respect to our mate- 
rial are quite otherwise. For years it has been customary to make 
all pollinations in the afternoon, in the belief that most pollen was 
shed in the early morning and was well out of the air at the time 
pollinations were made. It is difficult to reconcile the results of 
our regular practice with the facts disclosed by this age-of-pollen 
experiment, and further investigation is essential to gain enlighten- 
ment on these matters. 
From the standpoint of methods of measuring crossing over, it 
is of interest to observe that with such widely aberrant Mendelian 
ratios as are obtained with old pollen Yule's coefficient of association 
{Q) provides a satisfactory index of the gametic proportions. 
Brink (4) has found that in material involving the I aleurone 
factor the ratio of waxy to nonwaxy seeds is modified in some man- 
ner by this factor. His 
conclusions as to the 
effect of this factor are 
based on the following 
procedure : 
«— +■ 
T+ 
H ». 
<-8> 
/<? 
20 JO 40 
Fig. 5. — Percentage of crossovers in female gametes of 
16 closely related progenies arranged in an ascending 
series of mean crossover percentages and plotted with 
a range of ± three times the probable error of the 
progeny means. The mean is indicated for each 
progeny by a short vertical line 
The four classes of seeds 
from an ear segregating 
for white and waxy and 
known to have resulted 
from the combination 
IWx iwx X iwx iwx were 
planted separately and 
crosses made between the 
combinations I i Wx ivx 
X i i wx wx and I i wx 
ivx X i i Wx iox. 
It was found that 
crosses of the former 
sort gave an excess of 
waxy seeds which in 
some instances reached 63 per cent waxy, and the latter combination 
gave a deficiency. Brink noted further that the increased number of 
waxy seeds was largely confined to the i i wx wx zygotes. 
Since / and W x were linked, an excess of waxy zygotes would be 
made up largely of the class i i wx wx, and in the absence of the 
detailed figures it is possible that Brink's excess of this combina- 
tion is due to the linkage of these genes. With this interpretation, 
his results agree with ours where an excess of Avaxy seeds, brought 
about through devitalized pollen, was accompanied by an increase 
in the percentage of white seeds. If this were not the case, the 
linkage relations of / and Wx would be modified profoundly in 
those cases where an excess of waxy seeds occurred. 
With our material involving the C factor (a gene closely linked 
with /) there is no evidence that the nature of this factor has any 
effect on the ratio of waxy to nonwaxy seeds, Thus the ears shown 
in Table 18 are made up of the combination c c wx wx X C c Wx wx, 
a combination that corresponds to Brink's case where an excess of 
waxy seeds was found. Our results show that when fresh pollen 
is used there is a significant deficiency of waxy seeds, though if the 
