295 
build up its own structure, and it weakens or destroys a 
part of the leaf tissue. The effect in part is shown in the 
premature ripening and loss of the foliage. On young trees 
the leaves often begin to fall by the first of August, and 
frequently by the latter part of the month very few, except 
some of the youngest at the ends of the branches, remain 
on the tree. The early loss of foliage tells upon the vigor 
of the tree, and seriously interferes with the annual growth; 
at the same time the tree is ill prepared to withstand the 
rigors of winter, and starts into leaf the next spring with 
diminished vitality. According to Mr. T. T. Lyon,! the 
well known fruit grower of Michigan, all varieties are not 
attacked alike: ‘‘the Chicasaw and Americana classes are 
nearly or quite exempt, while many of the Domesticas, such 
as Bradshaw, Damson, Bavay, are far less liable to such at- 
tacks than Washington, Green Gage, Jefferson and numer- 
ous others.” Still he thinks that ‘‘the disease is a very 
serious one.” 
If we turn to find some means for checking or preventing 
the growth of this fungus, it becomes at once apparent, that 
so far as our present resources go, no topical application 
is likely to be efficacious, from the fact that it is not a super- 
ficial parasite, but an internal one. Some indirect method 
of fighting it must therefore be devised; for this purpose a 
knowledge of the transformations and habits of the fungus 
is evidently of primary importance. To this end a study of 
its life history has been carried on for two years past, but. 
up to the present time, it is to be regretted, without com- 
plete success. 
First, directing attention to the manner in which the 
fungus passes the winter, it is found that the septoria 
a spores (shown in Fig. 6) 
h| ra cease to be formed with 
IR the death of the leaf, and 
are replaced by another 
kind, which considered 
independently would be 
referred to the genus 
S&S Phoma. The latter are 
Fig. 8.—Part of the spore-bearing layer minute, colorless, nearly 
lining a phoma pustule; from a plum globular spores, formed 
leaf gathered in September. Magnified in the greatest abundance 
430 diameters. Original. at the ends of crowded 
vertical threads lining a cavity (Fig. 8). The external ap- 
pearance is that of black pustules which are borne on the 
same spots that. bore the septoria, and in equal abundance. 
Like the septoria, the phoma only fruits upon the under 



‘Mich. Horticulturist, Vol. I, 1886, p. 134. 
20 
