, Conn. Photo by Louis Buhle, Brooklyn Botanic Garden. Sept. 26,
1952.]

A study has been made of the factors that cause the Chinese and Japanese
chestnut to be resistant to the Endothia canker, and a close correlation
was found between the tannin content of the bark and the relative
resistance of the three species, i.e., Chinese, Japanese and American
chestnut. The total tannin concentration in the bark of the Asiatic
species is only slightly higher than in the American, and native trees
can be found with as high a concentration as is found in the Asiatic. A
similar overlap in resistance does not occur and it is therefore clear
that the total tannin concentration as such cannot account for
resistance. There is, however, good evidence that the tannins in the
Asiatic species, as a result of the way in which they are bound to other
colloids in the cells, are more soluble than in the American species.
This, of course, would have a marked bearing on the effectiveness with
which the tannins could check the spread of the parasite. Furthermore,
it has been found that the types of tannins in the three species differ.
In the American and Japanese species they are a mixture of catechol and
pyrogallol tannins, while they appear to be pure pyrogallol tannins in
the Chinese species. Considering the specificity of the enzyme systems
of fungi it is quite possible that different tannins show different
degrees of toxicity to a certain fungus. The following hypothesis has
been suggested to explain the relative resistance of the three species:
In the American chestnut bark the concentration of the available toxic
tannin never reaches a level where it can stop the advancing parasite.
The tannins in the Japanese species, although of the same type as in
the native tree, are more soluble and reach a level toxic to the fungus.
In the Chinese trees all the tannins of the bark belong to the toxic
pyrogallol groups, and this, combined with their high solubility,
results in the high degree of resistance in this species (4).

The information available at present regarding the formation of tannins
in plants is not conclusive. In some plants, apparently, they are formed
in the leaves, and the presence of carbon dioxide and light is required;
in other plants the tannin concentration can increase when the plants
are grown in darkness (5). A more general formation of tannin in tissues
with a high metabolic rate throughout the plant has also been suggest