2 3o ON A NEW CANKER-DISEASE OF PRUNUS YEDOENSIS, etc. 
500 grams of peeled potatoes were sliced as thin as possible and cooked in 
500 c. c. of water for one hour, then strained through cloth. 15 grams of 
agar were melted separately in 500 c. c. of water. The two were mixed and 
enough water was added to make a total of iood c. c. It was boiled suf- 
ficiently in Koch's steam sterilizer and then filtered through cotton. Even 
if prepared by the same method, when the standard media had been made 
in many different flasks, they were thoroughly mixed just before they were 
divided into small flasks, in order to add the tannic acid. 
I grew the causal fungus and the other two fungi mostly on slant test 
tubes and partly on the plain standard medium in Petri-dishes or Erlenmeyer's 
flasks, as checks for comparison, and also on the same medium to which had 
been added the following percentages of tannic acid : 0.1,0.2,0.4,0.8, 1.2, 
2.0, 5.0, 8.0, [i.o, 14.0. These cultures were made in November, 1914 and 
the observations were continued to April, 1915. From the results of these 
investigations I obtained the following informations: 
(1) The growth of any of these fungi causes no darkening of the 
standard medium, when tannic acid is not added; while if it is added, even 
as little as o. 1 %, a darkening of the medium takes place. Such a fact was 
observed by Clinton 0 , in the case of cultures of the chestnut-blight-fungus, 
and he proposed that this darkening indicates an oxidation of the tannic acid 
by the fungus, since those tubes without the introduction of the fungus remain 
undarkened except with the higher percentages, when they color as soon as 
made, upon cooling. 
(2) The medium in the tannic acid tubes remains liquefied when 0.8 °/ 0 
or more of tannic acid is added. 
(3) Cultures of this causal fungus in media containing o. 1, 0.2,0.4% 
of tannic acid show a more vigorous growth than the check cultures of potato- 
juice-agar without tannic acid. In tubes, which contain 0.8 % of tannic acid, 
the fungus also grows vigorously, and tends to form a more or less firm 
coating over the surface, after the manner of growth on the solid medium; 
but it is only after a long time that it begins to show the ordinary mode of 
