Aug. 26, 1918 
Variation and Correlation in Wheat 
369 
order for this group of characters is shown in the frequency distribution 
graphs (fig. 1, 2). For each of this group of characters the lowest mean 
occurs in 1914, the season least favorable to normal development during 
the latter part of the growing season, and the means for the other three 
years occur in ascending order according to the favorableness as a whole 
of the growing season for wheat, 1916, 1917, and 1915, respectively. 
The means for number of culms per plant are 2.651 ±0.019 * n I 9 I b> 
2.847 ±o.o 20 in 1917, 3-6o6±o.o63 in 1914, and 6.977±0.053 in I 9 I 5- 
The means for yield of straw, total length of culms, and total length of 
spikes per plant are in 
practically the same 
order as those for num¬ 
ber of culms. 
For number of culms 
per plant representing 
this group of charact¬ 
ers, the order of the 
means is shown in the 
frequency distribution 
graph (fig. 3). The 
magnitude of the means 
for this group of char¬ 
acters is largely depen¬ 
dent on the favorable¬ 
ness of conditions for 
growth during the early 
part of the season. 
Thisorderis 1916,1917, 
1914, and 1915, re¬ 
spectively. 
Comparison of the order of the means for the two groups of characters 
throughout the 4-year period shows the means for the group of characters 
represented by height of tallest culm, which are dependent for their 
development upon conditions during the latter part of the growing 
season, follow the order of optimum conditions during that time; and 
that the means for the other group of characters represented by number 
of culms, which develop largely during the early part of the season, 
follow the order of the best conditions for early growth. 
The means for average weight of kernel are i4.86o±o.i56 in 1914, 
23.732 ±0.056 in 1916, 27.563 ±0.118 in 1915, and 34*°5°±o.057 in 19 
The frequency distribution graph (fig. 4) shows this order. In 1914 and 
1916, the sequence of the means for average weight of kernels is the same 
as yield of grain and number of kernels; but in 1915 and 1917 in the 
reverse order. The kernels of the 1914 crop were shriveled, as were also 
some of those of the 1916 crop. In 1915 and 1917 all kernels were well 
filled. Under the especially favorable conditions which prevailed 
Fig. 3. —Graphs showing the frequency distribution of wheat plants 
for number of culms. 1914-1917. 
t 
