304 BOTANICAL GAZETTE [APRIL 
cannot be a factor in this disease as it seems to be in others (10, 
II, 33, 34). No varietal differences in the nitrogen content and 
forms of nitrogen are discernible in fig. 7. 
Discussion and summary 
The laboratory inoculations recorded in this paper corroborate 
the field observations on plum varieties as to their relative resistance 
to the brown rot fungus, Sclerotinia cinerea. In the field an 
important factor in resistance is the thickness of the skin. In the 
present studies this was eliminated by injecting the spores into the 
tissues, so that the differences in the rate of rotting were due mostly 
to physiological factors. The object of the investigation was to 
throw some light on these factors. The varieties showed not only 
different rates of rotting, but the character of the growth of the 
fungus differed as to the amount of fruiting. The susceptible 
varieties in general showed a greater amount of fruiting on the 
surface of the fruits. No study is recorded in the literature of the 
factors affecting sporulation in this fungus, except the vitamine 
relations touched upon by one of the writers (52). In the present 
work it was noticed that the juices of resistant varieties have a 
higher specific gravity, a slightly greater H-ion concentration, a 
lower titratable acidity, and a slightly greater oxalic acid content. 
In these items the differences between resistant and non-resistant 
varieties are not sufficiently marked to convince one that they 
constitute the chemical basis of resistance. Culture work with 
Sclerotinia, using fruit juices in which the various factors can be 
varied and controlled, will no doubt throw considerable light on 
the question. 
When the fungus rots the plum, some well marked changes in 
composition take place in the tissues. The juices show consider- 
able decrease in specific gravity, a decrease in true acidity, a 
decrease in titratable acidity that is of greater magnitude than the 
decrease in true acidity, and an increase in oxalic acid content. 
The fungus in some way prevents the production of tannin that 
takes place in the green fruit after it is picked from the tree. The 
fungus converts a portion of the non-protein nitrogen of the host 
into protein nitrogen in its own mycelium. 
