37^ 
Journal of Agricultural Research voi. xxm, no. 3 
The most evident fact revealed by the data is that there is no significant 
difference in the P H values of the juice of resistant and of susceptible 
varieties of wheat. It is rather surprising that there is so little differ¬ 
ence between the reactions of plants of varieties such as Kanred, Little 
Club, and Preston wheats, and Khapli emmer, representing not only 
the extremes of susceptibility and resistance to rust but also extremes of 
morphological characteristics. Another striking fact is that there is 
little variation in the reaction of the juice of the plant at different stages 
of growth. The averages show a slightly increased acidity of the green¬ 
house seedlings 2 to 4 weeks old over that of the same plants 1 week old, and 
but a small further increase as the plant matures. Environmental factors 
produce changes in reaction far greater than any due to age or variety. 
Table II gives the detailed results by varieties, the grouping showing 
how they were paired for close comparison. Extra care was taken to 
grow the plants constituting each group at the same time and under 
identical conditions. The necessity for such precaution is illustrated 
by the data on germinator seedlings, which show appreciable differences 
between certain groups. These are not in any case to be taken as 
indications of varietal differences, but as indications of the effects of 
small differences in the conditions under which the groups were grown. 
Tabi,S II.— Hydrogen-ion concentration , in P B units, of the expressed juice of some 
wheat varieties resistant and susceptible to stemrust 
Variety. 
Age and place of growth of seedlings. 
Name. 
C. I. 
No. 
Resist- i 
ant or 
suscep¬ 
tible,** 
7 to 10 
days in 
germi- 
nators. 
1 to 7 
weeks 
in 
green¬ 
house. 
4 weeks 
in 
green¬ 
house, 
un¬ 
limed 
soil 
4 weeks 
in 
green¬ 
house, 
limed 
soil. 
3 . 
months 
in 
green¬ 
house, 
limed 
soil. 
6 to 8 
weeks 
infield, 
poor 
growth. 
Kanred. 
5146 
iSS8 
R 
6.01 
3-87 
3-84 
Turkey. 
s 
6.01 
5-87 
6. 16 
Kanred.... 
smg 
1442 
R 
5 - 95 
3 - 93 
3-84 
3-84 
Kharkov. .. 
s 
Pentad (D-5). 
33 2 2 
4066 
4013 
R 
5 - 99 
5 - 92 
S -96 
s -»7 
5-87 
5- 81 
5. 81 
5 * 77 
5.81 
6.08 
5. 88 
5* 61 
Little Club. 
s 
6.18 
Khapli. 
R 
6.16 
3 - 74 
3-48 
Kota. 
5878 
3081 
R 
6.05 
6.08 
5-83 
5-79 
5 - 77 
5 - 72 
6.17 
6.12 
3-83 
3 - 76 
3 - 39 
5-33 
Preston. 
s 
Mindum. 
5296 
4064 
R 
S -98 
S -98 
3-88 
3 - 87 
6.07 
6.11 
3-81 
3-73 
5 - 5 * 
3-35 
Amautka. 
s 
Iumillo. 
1736 
R 
3-93 
3-93 
6.13 
5 - 72 
3-34 
Averap-e.. 
5 * 99 
3 -83 
3 -81 
6.13 
3-78 
3-53 
<* R—resistant; S— susceptible. See column 3 of Table III. 
The remarkable agreement between the values obtained for varieties 
representing widely varying morphological types is strikingly brought 
out in Table II. Consideration of the figures for any group in any column, 
and of the results as a whole, leads to the conclusion that varietal resist- 
