CHESTNUT BARK DISEASE. 367 
with age from light-orange through almost crimson- to dark 
chestnut-brown. The interior of the pustules is usually lighter 
colored, and more uniformly remains of a yellow tint. When 
fully matured, the fruiting pustules show small black dots on 
the surface or in cross-section, which are the ducts through 
which the matured spores escape. 
On the wood, the fruiting pustules are usually simple, smaller, 
conical in shape, and apparently do not produce the mature 
stage of the fungus. They have an appearance to the eye 
quite different from those on the bark, and for this reason 
Saccardo formed a distinct genus, Endothiella, for them. 
The pustules, within inconspicuous cavities, soon begin to 
form a summer, or conidial, stage. This, if it were the only 
stage produced, would place the fungus in the imperfect genus 
Cytospora, so this is sometimes known as the Cytospora stage 
of the fungus. The spores are produced apically in great 
numbers from slender fruiting threads. When filling the cavi- 
ties and swollen by moisture, they ooze out over the surface 
of the pustules as drops, or more frequently, slender yellowish 
tendrils. These tendrils are most conspicuous in summer just 
after rainy weather. Soon, however, they become worn or 
washed away by rains, and, if carried to cracks in the bark, 
they cause new infection. 
As the spore masses are viscid and moist, they easily adhere 
to insects, especially when crawling over them in the larval 
stage, and to the feet and beaks of birds, and these are con- 
sidered means of spreading infection, not only in the neighbor- 
hood, but also to distant points. These spores, Plate XXVIII i, 
are very minute, in fact, so small that it would take two or 
three hundred million to cover an: area an inch square. They 
are hyaline, oblong, unicellular with rounded ends, and about 
2.5-4.X0.75 p in size. 
In the same fruiting pustules that produce the Cytospora stage 
there appears, after some time, the mature spore stage, often 
called the winter stage, because it occurs most commonly from 
late fall to late spring. However, like the summer stage, this 
winter stage can be found more or less abundant at any time 
of the year, its appearance depending in part on the age of the 
fruiting pustules. With the beginning of this stage, the fruiting 
pustules have reached their maximum growth and the production 
