DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 495 



branches, or at the base of the tree, are evidences that the trees are 

 attacked by the chestnut blight fungus. 



The cankers on smooth bark are especially marked, and with a 

 reddish-brown color in contrast with the healthy bark can be seen for a 

 considerable distance (Fig. 171). As sunken, or swollen diseased areas 

 of the bark, they occur on branches of all sizes and generally the cankers 

 are ellipsoidal with the long ajds up and down the stem (Fig. 171). 

 The cankered areas of bark become covered with numerous small 

 pimples (Fig. 172) from which emerge in wet weather long twisted 



Fig. 174. — Chestnut blight fungus, £Mdo<A»a parasitica. A, Pustules on bark; 

 B, escape of pycnospores as gelatinous cords; C, D, magnified views of the cord-like 

 masses of pycnospores. (Frotn Gager after Murrill.) 



yellow horns of a gelatinous nature (Figs. 173 and 174). As the 

 canker ages the bark splits and cracks, and in a year or two it peels 

 off from the tree leaving the wood exposed to the weather (Fig. 127). 

 The mycelium forms thick, fan-like mats in the bark and cambium 

 of the tree and it spreads both longitudinally and circumferentially 

 (Fig. 17s) until, having completed its growth around the stem, or 

 branch, and kiUed the cambium and bark, the part of the tree above 

 the girdled portion succumbs and the next year leafless branches 

 show the irreparable damage done to the tree by the blight fungus 

 (Fig. 127). 



