168 
the circumference are likely to be arranged in circles. It not infrequently 
happens that 1 the pustules are not black at first, especially when the 
apples have been kept in a moist environment. They may appear quite 
white before they break through the cuticle, and later the spore masses 
give them a pink color over the top. Sections through diseased apples 
show that the tissues are decaying for some distance; and in preparing 
a partly decayed fruit for eating, great care must be takeu to remove 
every fragment of this discolored tissue, as a scarcely perceptible 
amount can impart an intensely bitter taste. 
On the grape .—The fungus seems to attack only ripe grapes, and when 
the diseased grape is a purple one no change of color occurs, but the 
berry decays and the skin seems to be raised up in pustules over the 
diseased portions. On white grapes the fungus produces a very charac¬ 
teristic appearance. A small, reddish-brown spot appears on the side 
of the berry; this spreads and becomes darker in the center, so that 
by the time it has spread over half the berry it has a purplish center 
merging into a narrow bright-brown border. It is moreover covered 
with minute pustules which are at first whitish, then exude a flesh- 
colored powder, and finally become dark brown or even black with age. 
The berry finally becomes quite dry and shriveled, but even in this con¬ 
dition it does not become black like those attacked by black rot, but 
may even preserve a translucent appearance. On a few grapes, whose 
tissues were at the same time hardened by the presence of the mycelium 
of Peronospora viticola , the areas attacked by the Gloeosporium had 
sunken in, as is the case with the apple. On the grape the pustules 
often continue bearing spores, and hence retain their flesh-colored aj)- 
pearance even when the berry is nearly all dried up. The fungus does 
not communicate a bitter taste to this fruit. 
MICROSCOPIC CHARACTERS. 
The structure of the fungus is so variable that it is almost impossible 
to frame a description that will be true under all circumstances. 
The appearance of the fruiting bodies differs on nearly every berry 
that the fungus attacks, although it is a somewhat curious fact that 
the pustules on any one berry are very nearly alike. The color and 
shape of the spores are the most constant characters, but the latter 
varies considerably. In the following description the most character¬ 
istic and common variations will be noted, but they by no means com¬ 
prise all that may be expected even in a short study of the fungus. 
The first stage in the formation of the fruiting body is the most constant 
one. A cushion of stroma forms just below the upper wall in a group 
of the epidermal cells; as it increases in size the contents and lower wall 
are pushed downwards, the cross walls are broken or absorbed, and the 
upper wall pushed upward until it is ruptured and the fungus exposed 
to the air. As soon as the strpma has attained about 20 p in thickness 
it can be seen to consist of parallel threads arranged at right angles to 
