108 BOTANICAL GAZETTE [SEPTEMBER 
two varieties in each section, indicated by 9 and 18, are resistant; 
the next two are non-resistant. Some of the rotted samples are 
missing, due to loss by contamination. It will be seen that the 
crude fiber is markedly higher in the resistant than in the non- 
resistant varieties, but all other constituents are lower. This 
relation holds in both the sound and the rotted samples, although 
data for the latter are available for the first stage only. VALLEAU 
(4) reports a positive correlation between firmness of the plum 
flesh and its resistance to brown rot. The firmness is due to the 
structural elements of the tissue, the cellulose cell walls and the 
pectic middle lamellae. Only the former are represented in the 
determination of crude fiber. From the results at hand it appears 
quite probable that the quality and quantity of cellulose material 
are important factors in resistance properties, although the pectic 
substances also play a part in the metabolism of this fungus, as was 
pointed out in a previous paper of this series (5). In what ways the 
middle lamella may play a part in resistance properties is not 
known. Since it is a compound of pectin with calcium, it was 
thought that determinations of calcium in the present samples 
might throw some light on the question, but the data show that 
calcium is higher in the susceptible varieties in about the same 
magnitude as the ash and nitrogen, and no special significance can 
be seen in it. 
In fig. 2 can be seen certain changes in the composition of plums 
during the course of ripening. As maturation progresses, the ash, 
nitrogen, and calcium steadily decrease. This is probably due to 
large increases in the soluble carbohydrates and organic acids. 
The crude fiber is somewhat higher in the second stage, which is 
just previous to full ripeness. The Compass variety is conspicu- 
ously low in crude fiber, and it is very susceptible to rotting by 
Sclerotinia. In table I the data on rate of rotting show the same 
tendencies as were discussed in the preceding paper of this series, 
namely, that the resistant varieties succumb to the rot much more 
slowly, and when rotted have a much firmer texture than the 
susceptible varieties. 
Conclusions 
1. Plum tissue that has been rotted by Sclerotinia cinerea is 
consistently higher in ash, CaO, nitrogen, and ether extract than 
