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AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
Fig. 12. Soil acidity and infection — pn 7.2, pH 7.5, pn 7.8, check. 
Re-isolations were made from several typical lesions from each flat, and 
pure cultures of Gihberella Saubijieiii were invariably obtained. The two 
control fiats containing the original uninoculated soil showed a perfect 
stand and no diseased seedlings. In table 7 a summary of the data is pre- 
sented. These data are also shown graphically in figure 14. For an ex- 
periment of this type the curve is very uniform. A maximum appears 
at Ph = 4.0, followed by a clear-cut minimum at pn = 5.5. As the more 
alkaline soils are reached the curve rises, and in the most alkaline infection 
is as high as 100 percent. 
Fig. 13. Soil acidity and infection — pH 8.2, pH 8.6, pn 9.0, check. 
Experiment 5. In the above described experiment a control or uninocu- 
lated soil was not used for each soil acidity, and the depression in the curve 
might be caused by the sulphate ion. A second experiment was therefore 
performed in which hydrochloric acid was used in place ot sulphuric acid 
in adjusting the soil reaction, and a flat of uninoculated soil at each acidity 
was used as a check. 
