(358 BOTANICAL GAZETTE : [NOVEMBER 
the entire time. A very few pycnospores were produced on the 
I per cent, but not on the others. 
This was the most toxic extract used in the entire series of 
experiments. / 
In order to test the possibility of preparing from commercial 
sources a compound similar in its effects to KERR’s extract “A,” 
a tannin compound was made as follows: tannin (MERCK) 60 gm., 
dextrose 10 gm., gallic acid 7 gm., arabinose 8 gm., total 85 gm. 
This material was added to the agar in the same manner as was the 
tannin. The series of cultures prepared were at intervals of o. 2- 
3.0 per cent. The effect on the proteids was the same for this 
substance as for tannin. The higher percentages digested almost 
all proteids so that the medium was a clear liquid. Sowings were 
made with E. radicalis mississippiensis (STEVENS no. 2424), E 
radicalis (CLINTON’s E. gyrosa no. 7674), E. parasitica (American, 
CLINTON’s no. 7675, and the Chinese strain). 
It seems scarcely necessary to give a detailed statement of these 
results. In all cases, except the American strain of E. parasitica, 
pycnidial formation was greatly retarded. Growth was very 
similar to that obtained with MErcx’s tannin. 
Summary 
1. Results obtained with commercial tannin are not always 
comparable to each other or to those obtained from specially pre- 
pared extracts, because of variations in chemical composition and 
the presence of tannin-like substances other than tannic acid. 
Commercial tannins of the same brand differ in their behavior in 
culture media, as indicated by the growth of the various species 
of Endothia used in these experiments. 
2. Commercial tannin and tannin in the plant are not the 
same. No extract will be the same as the substances in the 
plant. 
3. Tannin is an anhydrous glucoside of gallic acid and is easily 
converted by hydrolysis into gallic acid and related substances. 
It is very doubtful if any culture medium can be prepared contain- 
ing as much pure, unchanged tannin as was put intoit. Therefore, 
we cannot know the exact percentage of tannin in a culture medium, 
