10 



The [ourxal ok Hkrkditv 



jf^'t^SKfaim 



AMKUK AN (IIKMNL i A11A( KED. 



This and the four following figures, showing stages in the progress of the bark disease, were 

 taken by Professor J. F. Collins at various points on Long Island. This photograph 

 shows where the disease has secured a foothold on some of the smaller limbs, which are 

 quickly killed. When the infection is on the smaller limbs, however, the rest of the tree 

 may survive for several years. (Figure 2.) 



parasite have been considered as pos- 

 sible retarding agents, but as these 

 same inseets appear to also distribtite 

 the spores, their controlling influence 

 is not likely to prove important. 



MANNER OF INFECTION 



When, in the Chinese chestnut, any 

 spores of the parasitic fungus gain 

 entrance into a wound on any jxart of 

 the trunk or limbs, they give rise to a 

 canker which jjcrsists on the tree, be- 

 coming deejicr year by year as healthy 

 wood is formed around it. In the 

 American chestnut, however, the canker 

 ra])i(lly enlarges until it girdles the tree. 

 If the i)art attacked hajjjK'ns to be the 

 trunk, the whole tree is killed, some- 

 times in as short a time as a single 

 season. If the smaller branches are 



attacked, only those portions beyond 

 the ]x;)int of attack arc killed, and the 

 remainder of the tree may survive for 

 several years. Ultimately, however, all 

 American chestnut trees that are at- 

 tacked, die completely (fig. 5). Figures 

 2, 3, and 4 show the typically ragged 

 appearance of such trees, due to the 

 fact that some branches are not yet 

 girdled and still have normal foliage, 

 while others arc dead. 



Limbs and trtmks with smooth bark 

 soon show cankers in the fomi of dead, 

 discolored, sunken areas, which con- 

 tinue to enlarge and become covered 

 more or less thickly with the yellow, 

 orange, or reddish brown ])ustules of 

 the fruiting ftmgus (figs. 6 and 7). 

 From these j^ustules masses of minute 

 spores (conidia) are commonly extruded 



