166 BOTANICAL GAZETTE [MARCH 
area, without a border of whitish or lighter colored dead tissue. 
In this case it appears almost like a tar spot on the normal green 
leaf tissue, and reminds one of some of the species of Rhytisma. 
Later in the season the cuticle which covers the stroma wears 
away and gives the spot an ashen appearance, which is most pro- 
nounced near the edge. These black spots may be so numerous 
as to practically cover the entire upper surface of the leaf. 
In addition to these black stromata, and much more prominent 
in the early stages of infection, although the reverse is the case 
later in the season, are the pustules of the conidial stage. They 
are quite abundant and conspicuous in the early spring, and it is 
hard to understand how they can have been overlooked for so 
long a time. They are subcuticular, irregular in outline, and 
dark, owing to the cuticle which is stained by the fungus, and 
which splits irregularly to allow the dispersal of the spores, which 
are extruded in small white masses. The pustules formed earliest 
seem to have but little or no stromatic base, although those formed 
later in the summer are almost invariably situated on a distinct 
stroma, which they may or may not entirely cover. This conidial 
stage will be discussed more in detail later. 
DEVELOPMENT OF STROMATA 
Beneath each one of the small, black, subcuticular stromata, as 
represented in fig. 13, early in its development, beginning about 
the latter part of May, there commences the development of the 
young perithecium of the causative fungus. The stroma now 
becomes somewhat looser in structure near its central region, 
beneath which the perithecium is to be formed. The normal cells 
of which the stromatic hyphae are made up are short, approxi- 
mately isodiametrical (fig. 16), and contain comparatively little 
protoplasm, which little soon disappears, except in the basal layer 
of cells, and in those which are actively engaged in extending the 
edges of the stroma. They are more or less olivaceous to dilute 
brown in color, the depth of the hue depending on the age of the 
cell, but the very dark appearance of the stroma is due principally 
to a dark coloring matter which is not present in the cell wall to 
any extent, but seems to be excreted by the cells of the fungus 
