Journal of Agricultural Research 
Vol. XI, No. 4 
Il8 
mined by inherent tendencies and is less susceptible to external or en¬ 
vironmental influences than the other characters considered, we should 
expect smaller seasonal fluctuations than in the case of the other char¬ 
acters. 
As to progressive changes, we may note that while the low-oil strain 
seemed to tend toward a 12-row type for some years, it appears that in the 
1910, 1913, and 1915 crops 14 rows of kernels are the modal value. That 
is to say, there is no longer good evidence that the low-oil strain is ap¬ 
proaching a condition where the ears have 12 rows of kernels as a modal 
value. The differences existing in 1905 have been well maintained, ex¬ 
cept in the case of the high-protein and low-oil strains and we have indi¬ 
cated above that these two strains did not differ significantly in several 
recent crops. It is fair to say in a general way that the differences in the 
mean number of rows of kernels existing in 1905 have not been signi¬ 
ficantly accentuated by the selection for chemical composition from 1905 
to 1915, although the mean of the differences is slightly greater in the 
latter half of the period. 
GENERAL, STATEMENT ABOUT DISTINCT TYPES 
Taken as a whole, it is found that distinct types, as shown by the mean 
length of ears, the circumference of ears, the weight of ears, and the 
number of rows of kernels, are so well established that in most cases we 
may assign an order of magnitude that persists well in such changes of 
environment as have been experienced in the 11 years of planting from 
1905 to 1915. While certain progressive changes have been noted above, 
the selections for chemical composition from 1905 to 1915 have not in¬ 
creased the difference in the mean values to such an extent that we are 
able to assert that the strains differ more with respect to these characters 
during the second half of the period than during the first half, although 
they certainly do not as a whole differ less during the second half than 
during the first half. In fact, as stated above, the differences of the mean 
length of ears and the number of rows of kernels are larger, by an in¬ 
significant amount, during the second half than during the first half of the 
period. 
STANDARD DEVIATIONS 
In general, the differences in standard deviations for the different 
strains compared to the corresponding probable errors are much smaller 
than the differences in the mean values for the different strains compared 
to their probable errors. 
Many of the differences in standard deviations do not persist well from 
year to year under differences of soils and seasons. Perhaps we may 
properly infer from figure 5, that, on the whole, of the four strains the 
low-protein strain has the largest standard deviation in length of ears, 
and the high-oil strain has the smallest standard deviation; but there are 
