Walker—Nature of Disease Resistance in Plants. 
237 
fluid containing the soluble tannin is thus formed; on the basis 
of the germicidal action of this fluid, the resistance of such fruits 
to parasitic attack is explained. Cook and Taubenhaus (22) in a 
later paper point out that many fruits lose their power of resistance 
very soon after removal from the plant. This loss of resistance is 
proportionate to the reduced activity of the enzyme. They extended 
their studies to the vegetable acids and found the toxicity of the 
latter to vary with the organisms'used. Tannic acid was the most 
toxic, but the character and the true importance of this substance 
within the living plant remains to be determined by future investi¬ 
gations. Valleau (80) found no correlation between tannin content 
of plums and their resistance to Sclerotinia cinerea. The investi¬ 
gations upon tannin and organic acids in relation to resistance, 
while suggestive, are still inconclusive. 
Anthocyans and Flavones in Relation to Resistance 
The pigments of the anthocyan class have been suggested in 
several instances as substances contributing toward disease resist¬ 
ance, but in most cases the evidence is only observational and 
is not supported by experimental investigation. Sorauer (69) 
noted that red potatoes are in general more resistant than white. 
Jones (42) says that many potato experts, American and Euro¬ 
pean, regard red, rough-skinned varieties of potatoes as less 
liable to rot than thin, white-skinned potatoes. He points out, 
however, that there is abundant evidence of high disease resistance 
coupled with a thin white skin. Voges (83) considered red color 
in apple fruits a protection against scab but the large amount of 
data to be found in literature does not bear out this statement. 
Comes (19) attributed certain cases of resistance to the occurrence 
of anthocyan but his evidence is not convincing. In this con¬ 
nection, it is interesting to note the work of Cook and Wilson (23) 
who studied the effect of ^‘commercial” tannin and extracts from 
chestnut bark upon the growth of the chestnut blight organism, 
Endothia parasitica (Murr.) And. & And. Results with “com¬ 
mercial” tannin were of the same general nature as those secured 
with other fungi by Cook and Taubenhaus (21, 22) noted above. 
Since “commercial” tannin was variable in composition and since 
it contained a certain percentage of impurities, extracts from 
chestnut bark were also used. Through the cooperation of Kerr, 
three extracts were made: “1-X”, described as the water soluble 
