exposed (Fig. 8). In small cankers the cone of diseased bark 

 may be quickly forced out by the rapidly formed calluses, which 

 heal and close the canker wound (Pig. 10). In some cases the 

 canker is superficial, never reaching the cambium, except, per- 

 haps, in a limited area at the point of infection. Such wounds 

 heal quickly beneath the dead bark, which clings to the tree as. 

 a sort of scab (Fig. 5). 



The canker manifests itself in different forms on different 

 parts of the tree. Those that grow on limbs are usually small 

 and circular. If the disease is very severe the canker may be 

 larger. These we designate as "pit" cankers (Fig. 11). Often 

 the dead bark remains as a sort of lid to the pit but is easily 

 removed with the finger or knife blade (Fig. 10). These pit 

 cankers, in most cases, heal over quickly and by the end of the 

 second year close the wound entirely. Aside from affording 

 entrance to rot fungi such cankers unless they enlarge do not 

 seriously affect the health of the tree. 



There is another form of the canker which frequently becomes 

 serious, called " crotch canker." It usually appears in the 

 crotches where the main limbs arise from the body (Fig. 12), 

 but may also appear in the secondary crotches well up in the 

 tree. In general characters they are similar to the limb and 

 body cankers. Owing to their peculiar position, water is re- 

 tained more readily in the dead bark, thus affording the very 

 best conditions for the entrance and growth of rot fungi. These 

 find easier access to the heart wood at the crotch than on the 

 limbs. It was observed that these crotch cankers heal much less, 

 readily and successfully than do the limb and body cankers. 

 Crotch cankers, unless promptly attended to, mean the almost 

 certain destruction of the trees. In some sections of the country,, 

 especially the Hudson river valley, they have been very serious- 

 Cankers are frequently formed about pruned stubs. (Fig. 13). 

 These will be discussed further under another heading. 



On the bodies of trees are often found large, irregular cankers,, 

 which originated from the " pit " cankers. They come either 

 from new infection in the spring or from the organism remaining 

 in the canker during the winter. Fig 9 shows how such cankers 

 are formed. 



