BIOCHEMISTRY OF PLANT DISEASES" 
IV. PROXIMATE ANALYSIS OF PLUMS ROTTED BY 
SCLEROTINIA CINEREA 
J. J. Wittaman anv F. R. Davison 
(WITH TWO FIGURES) 
In the third paper of this series (6) the literature bearing on 
the chemistry of plant diseases, especially the effect of disease on 
the composition of plants and the chemical differences between 
resistant and non-resistant varieties of the same species of plant, 
was reviewed in some detail. Since the present work is a continua- 
tion of the former, it will not be necessary to make reference again 
to the results of other investigations, except incidentally during 
the discussion. 
In the previous work on the brown rot of plums, caused by the 
fungus Sclerotinia cinerea, it was found that during the progress of 
the rotting the H-ion concentration of the sap increases markedly; 
that oxalic acid is produced, but hardly in sufficient quantity to 
account for the increased acidity; that tannin decreases during 
the rotting; that protein nitrogen increases, due probably to the 
protein formed in the fungus mycelium. Resistant varieties did 
not differ conspicuously from non-resistant varieties, so far as the 
analyses showed, except that the resistant varieties usually had a 
more acid sap, and that more oxalic acid was produced in them. 
The tannin content of green plums usually increases after picking 
from the tree, but infection by Sclerotinia entirely inhibits this 
increase. 
Experimentation 
In the present work the ordinary proximate analyses, together 
with the determination of calcium, were made, using four varieties 
of plums at three stages of maturity, grown at the University Fruit 
* Published with the approval of the Director as Paper no. 272, Journal Series, 
Minnesota Agricultural Experiment Station. Presented at the meeting of the Ameri- 
can Chemical Society, September 9, rg21. 
Botanical Gazette, vol. 74] : [104 
