New York Agricultural Experiment Station. 347 
soil, and (4) of the use of stable manure. Upon the first and second 
points the results are not specially convincing, but there seems to be 
no room for doubt that as regards the amount of moisture in the soil 
and the presence of stable manure both materially increase the 
quantity of scab. It is probable that stable manure acts chiefly by 
raising the percentage of moisture retained by the soil. Altogether, 
the result of the experiments seems to bear out the hypothesis of 
Schacht that the chief cause of potato scab is the deleterious action of 
soil moisture on the skin of the tuber; the incidental circumstances 
which favor the action cannot be discussed at this time. 
Plum-Leaf Fungus. 
A very full accouat of this fungus, its appearance, transformations, 
development and influence upon the health of the plum and allied 
trees, was given in the last report of this Station,* and it is only neces- 
sary at present to supplement that account by some additional items 
the result of later studies, especially in regard to the form and occur- 
rence of the perfect spores, and the value of topical applications for 
checking the spread of the fungus. 
It has already been stated that the fungus continues its growth after 
the leaves fall to the ground, the abundant production of spores on 
the green leaves being replaced, as winter comes on, by spores of a 
different sort on the now dead leaves, and the whole aspect of the 
fungus becoming changed; with the advent of spring another change 
takes place, and the life cycle is completed by the production of 
ascospores, the presence of which in any fungus is taken to indicate 
the highest development that the species attains. 
The course of development of the spores has been studied with a 
great abundance of material, provided through the kindness of Mr. 
William Smith, of Geneva, who permitted some ground, well covered 
with fallen plum leaves bearing the fungus, to lie uncultivated until 
after my studies were completed. As noted in previous years, the 
asci, or spore sacs, can be seen by the first of May, but without well- 
defined spores. 
The ascospores were found toward the latter part of May, and wera 
well developed by June 1st. These spores are linear, somewhat 
curved (not oblong, as stated in last year's report, p. 296), nearly the 
length of the sac, in which they are closely packed, and from which 
owing to their colorless and delicate walls they are with difficulty dis- 
tinguished when the sac is unruptured. Figure 3 shows a sac filled 
* Report for 1886, p. 293. 
