44 
Journal of Agricultural Research 
Vol. XXIX, No. 1 
The coefficients are: 
F 2 , 1922: 
At St. Paul, Minn.. 0.079±0.028 
At Mandan, N. Dak_ .051 ± .021 
F 3> 1923: 
At Mandan, N. Dak_ .104 ± .025 
The correlations are positive but 
small and hardly significant except in 
F 3 eh Mandan in 1923. The F 2 data 
show that the presence of awns and 
their length have but slightly less 
effect upon the yield under droughty 
conditions at Mandan than under 
humid conditions at St. Paul. The 
F 3 data indicate, although the correla¬ 
tion is small, that preference in the 
selection of awned plants rather than 
at random seems justified. 
YIELD AND STEM-RUST INFECTION 
Stem-rust infection is not necessarily 
an index to rust damage. The same 
ing amounts of infection. Data were 
obtained in this study in F 2 at St. 
Paul, Minn., and Mandan, N. Dak., 
and in F 3 at Mandan, N. Dak. The 
data from F 2 at St. Paul, Minn., in 
1922 are given in Table XL. 
The coefficients are summarized as 
follows: 
F,, 1922: 
At St. Paul, 
Minn _ 
-0. 082 ±0. 028 
At Mandan, N. 
Dak 
- . 009 ± . 020 
F 3 , 1923: 
At Mandan, N. 
Dak 
- . 042 ± . 025 
The correlations are negative, as ex¬ 
pected, but they are small and not sig¬ 
nificant. The infection of rust that oc- 
Table XL. —Correlation between yield of plant and percentage of stem-rust infection 
in F 2 material of the crosses of Kota and Hard Federation wheats grown at St. 
Paul , Minn., in 1922 
Stem-rust 
infection, 
per cent 
Yield of plant in grams 1 
Total 
1 
0. 5 j 
1.5 
2.5 
3.5 
4.5 
5. 5 
6.5 
7.5 
8.5 
9.5 
10.5 14.5 
1 
15.5 
5 
2 
1 
2 
1 
2 
i 
\ 
i : 
! ■ 9 
US 
2 r 
2 
6 
6 
4 
7 
5 
! 1 
! 40 
2/S 
! 4 1 
10 
12 
15 
11 
13 
10 
4 
! i 
3 
1 ; 1 
85 
3JS 
! 3 i 
14 
16 
23 
14 
12 
1 
2 
! 6 
1 
92 
4ft 
! 13 I 
27 
27 
i 
23 
25 
16 
7 
7 
! 2 
2 _ 
1 
150 
55_ 
1 i 
7 
7 
9 
3 
6 
6 
2 
1 
1 
I 
43 
65_ 
! 3 1 
23 
15 
15 
19 
7 
8 
4 
1 
1 
75 
! I 
4 
7 
7 
4 
6 
3 
. 
31 
8iS 
1 ! 
4 
2 
2 
2 
2 
1 
1 
1 
16 
95 
1 f 
1 
1 
2 
-! 
Total.. 
29 j 
i : 
88 
97 
100 
86 
67 
46 
26 
13 
7 
3,1 
1 
564 
r=—0.082±0. 028 
percentage of stem-rust infection in 
different years may cause different de¬ 
grees of damage. An important corre¬ 
lation between rust infection and rust 
injury may be obtained when rust is 
the principal limiting yield factor. 
The years 1922 and 1923 were ones of 
general rust infection. The damage, 
however, varied with the time and 
amount of infection in different locali¬ 
ties and with the stage of growth of 
the wheat plant. A correlation study 
between the percentages of stem rust 
and yield of plant furnishes a method 
of determining rust damage from vary- 
curred in these experiments, therefore, 
had little or no effect on yield. An op¬ 
portunity for selection of resistant 
plants was offered, however, the im¬ 
portance of which is in no way lessened 
by the results of these correlations. 
It is important to determine how the 
average infection of F 3 strains is corre¬ 
lated with that of F 2 plants. The data 
presented in Table XLI show that a 
large, important, and significant coeffi¬ 
cient of 0.674 ±0.018 was obtained. It 
may be concluded, therefore, that the 
resistance to stem rust that occurred is 
inherited. 
