Apr., 1922] HOPKINS HYDROGEN-ION CONCENTRATION 
Table 9. Relation of Soil Acidity to the Number of Seedlings Up in Four Days in the Inocu- 
lated and Uninoculated Series 
Seedlings 
up 4 Days 
Controls 
0 
0 
0 
I 
4 
12 
I 
2 
4 
16 
29 
57 
53 
38 
5 
9 
Seedlings 
up 4 Days 
— Inocu- 
lated 
Series 
0 
0 
0 
0 
0 
0 
2 
4 
0 
15 
21 
26 
27 
30 
I 
0 
3-8 
4-35 4-56 
4.89 
5-25 
5-37 
5-4 
5-47 
5-57 
5.71 6.3 6.91 
7-25 
7.8 
7.82 
Although there is only slight evidence of a minimum in the inoculated 
series, due perhaps to unfavorable greenhouse conditions at the time this 
experiment was run, the uninoculated series shows a distinct minimum at 
about Ph 5.5. This indicates not only that the phenomenon of this minimum 
is related to infection, but that there is an independent action of the soil 
acidity on the germination of wheat. 
The first signs of infection at the surface of the soil were noted nine 
days after planting. The final data were taken at the end of three weeks. 
The plants were all removed as in experiment 4, and the percentage of 
infection was determined. These data are presented in table 10 and are 
shown graphically in figure 18. The pH values in this case are the averages 
of three series of determinations. The temperature during this experiment 
varied from about 12° C. to 30° C, with an average of about 19. s"" C. 
