3 



mirnoi-ous in ihe diseased bark lliat as inyceliuiii, llu-v may be set n 

 with the nailed eye, clustered togetlier in the form of small, butl- 

 coloied, fan like bodies when the bark is pared down. These fungal 

 threads feed in the living tissues of the bark an<l eventually grow into ' 

 the sapwood. Wherever they gnnv they cause the speedy death of the » 

 living cells of the trees. After a time the fungus completely girdles 

 the tree, trunk or branch on which it is feeding. This causes the death 

 of that i»art above the girdled portion, much as if girdled with an axe. 



When the fungus has grown for a time in the chestnut bark, 

 it develojis on the surface of the latter a series of tiny, irregularly 

 dome-shaped protrusions, (called jjustules), each rarely larger than 

 the head of a pin. These are the fruiting bodies which produce mil- 

 lions of sticky spores corresponding to seeds, and so tiny that they 

 can be seen only by means of a powerful microscope. On smooth, 

 young bark these pustules usually tii-st appear as little reddish blis- 

 ters beneath the surface of the bark. The tops of these blisters 

 soon burst and the pustules appear as slightly raised spots covering 

 the surrounding dark colored bark. On somewhat older bark the 

 infected portions often, (though not always), become sunken as a 

 result of the de;struction of the underlying tissue. On small branches, 

 especially young shoots, the infected portion is often abnormally 

 thickened and cracked, and of a brilliant reddish or orange color. 



Two forms of spores are produced, as in many other fungi. During 

 and immediately following damp weather the mature, pustules be- 

 come somewhat enlarged, and thrust out slender twisted threads or 

 "sporo horns," one-sixteenth to three-eighths of an inch in length, 

 and occasionally nunli longer. These are composed of the very 

 minute summer spores held together by mucilaginous matter. At 

 first, these threads are soft and jelly-like but they soon become hard, 

 and, when dry, brittle. The number of spores in one of these "spore- 

 horns"' is so great that a single one, a ([uarter of an inch long, has 

 been estimated to contain over five million individual spores. 



The winter spores, (or ascospores), are more frequently produced 

 during the fall and winter and are larger and less numerous than 

 the summer spores. They are forced from the enchasing sacs in the 

 mature pustules in damp weather and may be very important factors 

 in spreading the disease. 



DISSEMINATION 



The blight usually appears first upon a tree here and there some " 

 miles ahead of the general infection. Where these instances of in- ^ 

 fection in regions ahead of the line of general advance are found, it 

 may be that the sticky spores of the fungus have been carried 

 on the feet of birds, particularly woodpeckers and other insectivorous 

 birds. When these spores are deposited on healthy trees they are 



