CHESTNUT BARK DISEASE. 407 
year to year according to external conditions more or less 
favorable for its production. 
In our tannic acid culture work with the true chestnut blight 
and its close ally, Endothia gyrosa, reported in detail later on, 
we found: (1) Both fungi can use tannic acid, at least in 
small amounts, as food,—shown by the blackening of media 
through oxidation, loss of acidity, more luxuriant growth, with 
a low per cent. of the acid added, than without it, and a slight 
growth on agar-agar with tannic acid as the available source 
of food. (2) Higher percentages of tannic acid (four per 
cent. and above) are detrimental to a vigorous growth of 
either of these fungi, and finally (10 to 14 per cent.) entirely 
inhibit their growth. But with the true blight the tolerance 
is apparently greater by 2 to 4 per cent. than that of the 
saprophytic E. gyrosa. (3) Long-continued cultivation of the 
parasitic variety in artificial cultures without tannic acid prob- 
ably lowers its tolerance to the higher percentages of tannic 
acid. (4) Gradually passing these fungi in cultures from the 
lower to the higher percentages of tannic acid apparently 
raises their tolerance to it. 
From the results of these cultural experiments and what we 
have been able to learn about tannic acid in the chestnut, we 
reason that the true chestnut blight is better able to become an 
active parasite on chestnut trees than the Endothia gyrosa. Any 
cause that would lower the tannic acid, etc., content of the 
trees would allow it to develop into a more vigorous para- 
site, and its gradual tolerance to this higher percentage of 
tannic acid would give it an added virulence up to a certain 
extent. With the return of the tannic acid, etc., content of 
the tree above this limit of tolerance, the fungus would gradu- 
ally revert to-a less virulent and finally to even an inconspicuous 
parasite. 
PREVIOUS CHESTNUT TROUBLES. 
Nature of the Troubles. It is well known that in times past 
the chestnut trees in this country have suffered severely in cer- 
tain districts, particularly in the South, in some cases being 
practically exterminated, so that their range is now consider- 
ably lessened from what it was originally. Strangely enough, 
no one has surely accounted for any of these devastations. 
