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AMERICAN JOURNAL OF BOTANY 
[Voi. 9- 
Fig. 17. Hydrogen-ion concentration of soil and number of seedlings up in four days 
in uninoculated flats. Hydrochloric-acid series. 
Table 10. Hydrogen-ion Concentration of the Soil and Seedling Infection. 
Hydrochloric-acid Series 
No. of Flat 
Ph (Average) 
Total Plants 
Number Infected 
Percent Infected 
33 
3.5 
67 
48 
71.6 
42 
3.8 
50 
21 
42.0 
40 
447 
65 
50 
76.9 
49 
4-85 
58 
44 
75.9 
56 
5.12 
62 
37 
59.7 
41 
5-3 
61 
39 
64.0 
38 
5-43 
66 
31 
47.0 
55 
5-47 
69 
28 
40.5 
28 
5-47 
63 
22 
34-9 
45 
5-6 
70 
25 
35.7 
18 
5-74 
78 
32 
41.0 
24 
6.4 
79 
38 
48.1 
I 
6.98 
80 
39 
48.7 
3 
7.18 
75 
40 
53-3 
46 
7.83 
58 
45 
77.6 
43 
7.83 
69 
52 
75-3 
In the uninoculated flats an occasional infected seedling was found, 
due perhaps to natural infection from the seed. All others were uninfected 
at the time of digging. Examining the data given in table 10 as shown in 
figure 18, it can be seen that when hydrochloric acid is used in place of sul- 
phuric acid in the adjustment of the soil to various acidities, the same 
phenomenon occurs as was noted in experiment 4. A minimum in the 
infection is present at a pn of 5.5. This is strong evidence that the minimum 
in the infection curve is due to the hydrogen-ion concentration alone. This 
is strengthened of course by the results obtained in the growth of Gibberello 
Saubinetii, when an adjustment of the reaction with sulphuric acid, acid 
