Feb,3.1923 Hydrogen-Ion Concentration and Varietal Resistance 377 
ance to stem rust is not determined by the hydrogen-ion concentration 
of the cell sap. 
Included in the list of wheats of which the hydrogen-ion concentration 
of the juices is given in Table II are varieties resistant and susceptible 
to diseases other than stem rust. From data kindly furnished by Dr. 
E. B. Mains on leaf rust, Mr. C. W. Hungerford on stripe rust, Dr. E. C. 
Stakman on stem rust, Dr. E. F. Gaines on stinking smut, Dr. W. H. 
Tisdale and Miss M. A. Griffiths on flag smut, Dr. J. G. Dickson (winter 
wheats) and Mr. J. J. Christensen (summer wheats) on scab, and Mr. 
R. W. Leukel on nematodes, together with the results of personal ob¬ 
servations on mildew, Table III was compiled. 
Table III .—Resistance and susceptibility of wheat varieties to various diseases a 
Variety. 
C. I. 
No. 
Stem 
rust 
( Pucci- 
nia gra- 
minis 
tritici). 
Leaf rust 
(Puccmia 
triticina). 
Stripe rust 
( Puccmia 
glumarum 
tritici). 
Stink¬ 
ing 
smut 
(T ille- 
tia 
tritici ). 
Flag 
smut 
(Uro- 
cystis 
tritici). 
Scab 
(Gibber- 
ella 
saubi- 
netii). 
Mildew 
(Ery- 
siphe 
gram- 
inis). 
Nema¬ 
tode 
(Tylen- 
chus 
tritici). 
Field 
and 
green¬ 
house. 
Field. 
Green¬ 
house. 
Field. 
Green¬ 
house. 
Field. 
Field 
and 
green¬ 
house. 
Field 
and 
green¬ 
house. 
Field 
and 
green¬ 
house. 
Field. 
Kanred. 
5146 
R* 
R 
S 
S 
S 
R— 
R 
S 
S 
R 
Turkey. 
1558 
S* 
S 
— 
R- 
S+ 
R— 
R 
S 
S 
S 
Kharkov. 
1442 
s* 
R- 
— 
R 
R- 
R 
— 
S 
— 
— 
Pentad (D-5). 
3322 
R* 
R 
— 
R 
— 
s 
— 
S 
S 
Little Club... 
4066 
S+ 
S+ 
S+ 
S 
S+ 
S+ 
S+ 
— 
s+ 
— 
Khapli. 
4013 
R 
R 
R* 
R- 
R 
R- 
— 
R 
— 
Kota. 
5878 
R* 
S+ 
S-f 
— 
— 
ST- 
— 
R 
S 
s 
Preston. 
3081 
S* 
s 
s 
R- 
R 
R- 
— 
R 
S 
s 
Mindum. 
5296 
R—* 
R 
s* 
S 
— 
R- 
— 
S 
R- 
Amautka. 
4064 
S* 
R 
s* 
S 
S+ 
R- 
— 
R- 
s 
Iumillo. 
1736 
R* 
R 
s* 
s 
s 
— 
— 
— 
S 
a R — resistant; R— — only moderately resistant; S — susceptible; S+ — extremely susceptible; * — not 
susceptible nor resistant to all biologic forms. _ 
The variable behavior of these varieties with respect to infec¬ 
tion by the different organisms is interesting, especially since Vavilov 
(31) has come to the conclusion that if a variety is susceptible or 
resistant to one it is very likely to be correspondingly susceptible or 
resistant to all. The uniformly high susceptibility of Little Club and 
resistance of Khapli are the only examples in the preceding table of 
consistent behavior in this regard. 
From the data given in Table II and Table III, we can conclude 
that there is no correlation between the hydrogen-ion concentration of 
the expressed juice and varietal resistance or susceptibility to any of 
these diseases. The possibility that the total acidity of the cell sap may 
play an important r 61 e in the progress of the chemical reactions between 
the host protoplasm and the destructive secretions of the invading 
fungus remains and is now being investigated; but that the concentra¬ 
tion of free hydrogen ions is a determing factor is precluded by the data 
here reported. 
EFFECTS OF ENVIRONMENTAL FACTORS AND EXPERIMENTAL PROCEDURE 
ON THE HYDROGEN-ION CONCENTRATION OF WHEAT JUICE 
In the following pages are described a number of experiments designed 
to determine the magnitude of errors that are likely to be introduced 
into measurements of the hydrogen-ion concentration of plant juices, 
