INSECTS AND DISEASES OK THE PEACH 



1115 



localities, and in some cases has affected a majority of the trees in 

 the orchard. 



Why a tree should be subject to such injury at this point is not 

 clear. It will be remembered, however, that a section of bark 

 of the crotch of a tree is thicker than any other area on the tree. 

 It will also be remembered that the cells of this particular area 

 are highly active and specialized. It is suspected that trees af- 

 fected by freezing at the crotch have been extremely vigorous in 

 the previous summer, and their wood and bark have not ripened 

 properly. The frost thus gains access to the tree and injures the 

 cells. 



A similar canker is 

 likely to occur from 

 another source. Growers 

 are sometimes in the habit 

 of leaving a small dead 

 stub, a part of the original 

 trunk of the nursery tree 

 as set, in the crotch of the 

 tree. This stub seems to 

 be an ideal spot for one of 

 the deadwood fungi, a 

 Yalsa, to attack. The stub 

 becomes affected with the 

 fungus and Inter forms a 

 distant canker causing 

 very weak crotches. This 

 fungous canker can be 

 distinguished from frost 

 injury of the crotch by 

 the fact that in the former 

 case minute round-headed 

 fruiting bodies of the fun- 

 is form in the bark. In young trees all such stubs (Fig. 357, at 

 a) should be carefully removed as soon as the lateral buds of the 

 lowly set tree have started. Such forms of cankers are the most 

 frequent cause for the breaking down of trees in later years. 



FIG. 357. FrxorsEn STUB CANKER 



