•378 
Journal of Agricultural Research 
Vol. V, No. 9 
well covered with germinating spores, no instances were found in which 
the germ tubes gained entrance directly through the cuticle. 
Further evidence that the germ tubes do not usually penetrate the 
cuticle was obtained when two green plums of B X W 15, a very resistant 
variety, were scraped lightly with a sharp knife, thereby removing the 
cuticle without otherwise injuring the epidermis, and were then inocu¬ 
lated. These, with seven others of the same variety which had not been 
so treated, were sprayed with distilled water containing chlamydospores 
and put under a bell jar. At the end of 58 hours the two plums which had 
been scraped showed 10 and 13 spots, respectively, but rotted very 
slowly from the infection points. The seven unscraped plums were at 
this time without infection spots, but eventually three of these showed 
evidences of infection. 
Because of this method of infection, resistance can not be attributed 
entirely to morphological differences in the epidermis of the varieties. 
There are however, certain morphological differences in the stomata and 
lenticels which contribute to resistance, the nature of which will be dis¬ 
cussed later. When once the fungus has gained entrance the plums 
always rot more or less rapidly, depending upon the variety. 
FIELD OBSERVATIONS 
It is apparent from the facts given that the small amount of rot found 
in the orchard on green plums is not due to any greater resistance to 
infection which the green fruit may possess over ripe fruit. Neverthe¬ 
less, the brown-rot in the orchard causes the greatest damage as a ripe- 
rot rather than as a green-rot. 
It is a fact of considerable importance that it is not until the plums 
are ripe and begin to soften slightly that the fungus does its greatest 
damage as a ripe-rot. This is due probably to two reasons. The first 
is that there are greater possibilities of infection at this time. Field 
observations show that green plums will rot on the trees, owing usually 
to infection through curculio or other wounds, and that the rot will 
spread from one to another where they are in contact. Thus the number 
of rotted fruits and hence of infection sources to the ripe fruit is grad¬ 
ually increasing. Although there are other methods of infection, the 
largest number in ripe fruit is due directly or indirectly to contact with 
rotten green ptyms. It is very common in the field to find large groups 
of plums on a tree completely rotted, while other groups on the same 
tree are entirely free from rot. In these groups it is nearly always 
possible to trace the original source of infection back to one plum which 
has in most cases been infected through a wound of some kind while still 
green. 
Another source of infection, more common in ripe or nearly ripe fruits 
than in green fruits, is direct infection from spore suspensions in water, 
