2 5 8 



DISEASES OF TREES 



depth of an inch or two, and this is succeeded in a few years by 

 wound-rot, which, however, ceases to make progress when the 

 wound closes (Fig. 149). If pruning has been done in summer, 

 it will be found that beneath the wound brownness appears 

 in the youngest annual ring, and often spreads down the stem 

 for four or five yards. If one omits to apply a coat of tar, the 

 danger of infection by parasitic fungi is naturally increased. 

 These, however, penetrate even into tarred wounds should they 



FIG. 149. Oak pruned in July. 

 Rot has spread from and be- 

 neath the untarred surface of 

 the wound far into the stem. 

 One third natural size. 



FIG. 150. The occluded branch- 

 wound of an oak which has been 

 infected by Hydnum diversidens. 

 One half natural size. 



be formed in spring or summer, because at that time the germ- 

 tubes are able to enter beneath the lower edge of the wound 

 (Fig. 1 50). 



Tarring produces satisfactory results only when pruning has 

 been done in late autumn or in winter, because it is only then 

 that the tar is absorbed by the surface of the wound. It would 

 appear that the absorption of the tar is due partly to the 

 diminished amount of water in the wood during autumn, and 



