BIOCHEMISTRY OF PLANT DISEASES 
. III. EFFECT OF SCLEROTINIA CINEREA ON PLUMS! 
J. J. WILLAMAN AND W..M. SanpDstTROM 
(WITH SEVEN FIGURES) 
From the viewpoint that a fungus attacks a host plant, not to 
destroy it, but to gain a livelihood, it becomes of interest in the 
study of the chemistry of resistance to discover why a fungus can 
parasitize some varieties of a host and not others. There may be 
several bases for this difference: (1) the structure of the resistant 
host may offer mechanical difficulties to the entrance of the para- 
site; (2) the host may contain or produce repellent substances, 
such as tannins, acids, antienzymes, and antibodies; or (3) the 
host may fail to furnish the proper kinds and amounts of nutrients 
for the normal development of the fungus. 
Each of these possibilities has received some attention at the 
hands of investigators; but the two latter, constituting what may 
be called the biochemical basis of resistance and susceptibility, have 
received the least. It was decided, therefore, to attack the problem 
of resistance and susceptibility in plants from the standpoint of the 
nutrition of the parasite, using the brown rot organism of stone 
fruits, Sclerotinia cinerea, as the experimental organism. The first 
paper in this series dealt with the vitamine requirement of the 
fungus (52), the second with its relations to the pectic substances 
of the host (53); the present paper deals with the composition of 
certain varieties of plums, and the changes in composition brought 
about during the process of rotting by the fungus. 
Previous work 
Giese and TAUBENHAUS (16, 17) found that a great many fungi 
are very sensitive to tannin, and they believed that this could be 
a limiting factor in their ability to attack certain plants. In 
general, parasites are more sensitive to tannin than saprophytes. 
* Published with the approval of the Director as Paper no. 236, Journal Series, 
innesota Agricultural Experiment Station. 
287] [Botanical Gazette, vol. 73 _ 
