170 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
Seedlings began to appear in some of the flats at the end of three days, 
and at the end of four days the number of seedHngs in each flat was counted. 
The number of seedHngs with the corresponding pn values is shown in 
table 6. 
In figure 8 the data of table 6 are shown graphically. This curve is 
fairly uniform and shows a marked depression at a pH of about 5.5 with 
two maxima on either side, one at a pn of about 4.5 and the other near 
neutrahty (pn = 7.0). 
3 ^ S i f S «i 
P„ Soli 
Fig. 8. Relation of number of seedlings up in four days and hydrogen-ion concentra- 
tion of soil. 
It is not certain whether the variations in germination noted in the data 
in table 6 and in figure 8 are due entirely to the effect of variations in the 
hydrogen-ion concentration upon infection by Gihherella Sauhinetii. From 
experiment 5, however, and also from unpublished data secured by Dr. W. 
J. Robbins, it is very probable that, apart from infection, variations in 
the hydrogen-ion concentration cause the curve of the germination of wheat 
to pass through two maxima with a minimum between. 
Fig. 9. Soil acidity and seedling infection — the three most acid flats of soil, on left, 
compared with check flat on right; pn 3.6, pH 3.9, pn 4.4, check. 
