Apr., 1922] HOPKINS — HYDROGEN-ION CONCENTRATION I69 
The data given in table 5 are also presented in the form of a graph (fig. 7), 
which is a titration curve of this soil. The acid or alkali added to the flats 
was thoroughly mixed with the 18 kilograms of soil so that a uniform acidity 
would be obtained. The soil in seventeen of the flats was adjusted in this 
manner, two others being retained as checks. 
Fig. 7. Titration curve of soil used in experiment 4 with N/i NaOH and N/i H2SO4. 
The flats were allowed to stand for about a week, when soil samples 
were taken for acidity determinations. A cork borer was used in taking 
the sample, and several "cores" of soil were taken from various parts of 
the flat. They were thoroughly mixed to insure a representative sample. 
At the end of a week the flats were planted with wheat. 
A good sample of Fultz wheat was used. The seed, with the exception 
of that used in the two control flats, was shaken before planting with a 
spore suspension of Gihherella Sauhinetii from a single-spore culture. Ap- 
proximately 80 seeds were planted in each flat, in two-inch checks, two seeds 
per hill. The surface of the soil was then sprayed with a spore suspension. 
A fairly uniform moisture content was maintained by watering the flats 
with a fine spray from a garden hose. Observations were made of the soil 
temperature at frequent intervals. This averaged about 20° C. and varied 
from 20-25° C. A set of soil samples for hydrogen-ion determinations was 
taken at intervals of one week, four samples in all being taken. 
Table 6. The Effect of Soil Reaction on the Germination of Wheat Seedlings 
No. of 
Seedlings 
up in 4 
Days 
3 
16 
32 
33 
31 
41 
24 
39 
29 
38 
49 
55 
34 
34 
10 
0 
0 
Ph 
3.65 3.8 
4.25 
4-55 
475 5-4 
5.6 5-7 5-9 
6.4 
6.6 7.15 
7-45 7.75 
8.3 
8.65 
9.0 
