278 ON A NEW CANKER-DISEASE OF PRUNUS YF.DOENSIS, etc. 
branch, it was found that the amount of tannin is more or less increased in 
the diseased bark. It was thought desirable therefore to study the causal 
fungus in artificial cultures containing different percentages of tannin, to 
determine how it affected their vigor, growth and spore production. Accord- 
ing to the previous researches, tannin is said to occur in practically all parts 
of the plant, but reaches its maximum in the bark of trees. It varies in 
amount in different parts of the plant, and at different seasons of the year. 
It also differs in different plants, but all tannins, from whatever source, have 
many properties in common. Tannin has generali}' been supposed to be 
largely a waste product, which serves more or less as a protective agent against 
animal and fungus attack. A few writers have raised the question whether 
or not it might serve some use in the physiological activities of the plant, 
possibly in the way of food. For instance, Pfeffer (1897) 20) and a few 
other authors are inclined to consider the tannin as something more than a 
by-product. 
Pfeffer (1897) 205 says that fungi can assimilate many aromatic bodies 
such as tannin, resorcin, hydroquinone, phloroglucin, etc., but, except in the 
case of quinic acid, most of these afford very poor food materials ; and again, 
he adds, tannins and glucosides are undoubtedly produced for definite pur- 
poses, and are not mere by-products produced under all circumstances. 
Cook (191 1)% who studied the effects of tannic acid on different species 
of fungi in artificial cultures, says that the results of his experiments in some 
respects confirm the investigations of Massee, Ward and others concerning 
the positive and negative chemotactic action on the germ tubes of the fungi. 
By his report, it appears that tannin is an important factor and that its im- 
portance varies according to the other substances with which it is associated 
in the cells of the host plant ; and while tannin no doubt serves as a protective 
agent, its efficiency in this direction will vary somewhat with the character 
of the other substances within the cell. He thinks this may account for the 
variation in power of resistance between species, varieties, and individual 
plants. He further says : "The fact that plants which produce large quantities 
