Apr.. 1922] 
HOPKINS HYDROGEN-ION CONCENTRATION 
Table 7. Hydrogen-ion Concentration of the Soil and Seedling Infection. 
Sulphuric-acid Series 
JNo. 01 r lat 
Ph (Average) 
Total Plants 
Number Infected 
Percent Infected 
32 
6-^6 
70 
43 
56.6 
1 nr» 
77 
03 
C T Q 
ol.o 
25 
4-36 
03 
03 
75-9 
T A 
4-65 
70 
42 
60.0 
12 
400 
76 
32 
42.1 
35 
5-53 
82 
19 
23.2 
14 
5-66 
70 
39 
55-7 
17 
5.80 
73 
29 
39-7 
27 
5-90 
75 
41 
54-7 
15 
6.47 
80 
43 
53-8 
29 
6.67 
84 
44 
52.4 
II 
'J.22 
79 
42 
53-2 
31 
7.48 
82 
54 
65-9 
10 
7.78 
79 
39 
49.4 
13 
8.22 
79 
72 
91.2 
6 
8.63 
79 
79 
100.0 
22 
9.06 
77 
77 
100.0 
37 
Control 
80 
0 
0 
7 
Control 
81 
0 
0 
Fig. 14. Soil acidity and infection — hydrogen-ion concentration in its relation to 
the percentage of seedling infection — sulphuric-acid series. 
Another soil sample was used. Its reaction was adjusted in essentially 
the same manner as before. Using 2N HCl and 2N NaOH, a titration 
curve of this soil was constructed and the quantities of acid or alkali re- 
quired to secure the desired acidities were calculated for 36 kilograms of 
soil. After thorough mixing, the soil was divided between two flats, one to 
be inoculated and the other for a control. The titration data which are 
given in table 8 are the results obtained in the fiats after mixing the 36 
kilograms of soil in each case with the required amount of solution. The 
