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 

 2.5-4x0.75 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 



