[Vor. 4 
172 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
the case of Glomerella this is variable with the different decoc- 
tions. An attempt to standardize the sugar beet decoctions 
has resulted with every fungus in a slight decrease of growth 
in comparison with that in the natural decoction. On Ше 
кж whole, the prune 
FEF decoction has 
yielded less growth 
than either of the 
other three plotted 
in the curves ex- 
cept in the case of 
one organism, 
Macrosporium. 
E а a = та Un fortunately, 
Fig. 4. ages — = weights of cul- hydrogen lon de- 
tures in mg. on ordinates, solutions (see p. 166 for terminations were 
explanation) on кыйн. "Key to hes in fig. 1. not made at the 
time the eultures were installed, so that in order to ob- 
tain results for the original solutions it was necessary to pre- 
pare a second lot of the decoctions. These would undoubtedly 
correspond very closely to those employed for the cultures, 
and are therefore fairly suitable controls for changes in 
hydrogen ion concentrations occurring during the growth of 
the organisms. In this work the colorimetric method was 
employed, and it is unnecessary here to give the details of the 
method further than to say that the standard solutions of 
Sorensen, as modified by Henderson, as well as all available 
indicators of merit were used. 
With reference to the hydrogen ion concentration of the 
eontrol or original solutions, it is to be noted that little differ- 
ence was found between the natural decoctions of bean, turnip, 
prune, and potato, that is, after standardization,—all of these 
being approximately 10-*. These decoctions, moreover, were 
only influenced to a slight degree by the addition of sugar or 
nutrient salts as previously described. After standardiza- 
tion the sugar beet decoction was about 10-3 and the corn 
meal 102. It was evident, therefore, that the attempted 
standardization of corn meal to + 15 Fuller's scale actually 
