J92 



DISEASES OF TREES 



as 



and silver firs they may spring directly from the bark 

 well. 



The spores which are annually produced in these sporophores 

 are scattered by the wind, and should they gain a footing on a 

 fresh branch-wound which is not protected by a covering of 

 resin they push their germ-tube into the stem, and the mycelium 



FIG. 122. Part of the stem of a pine bearing the sporophore of T. Pini. a, healthy 

 alburnum ; b, wood saturated with resin in the neighbourhood of the sporo- 

 phore ; c, decomposed wood ; d, the canals in which the spores are produced ; 

 e, older canals which have become filled up by fungus-tissue ; /, the upper 

 surface marked by zones. One half natural size. 



spreads partly upwards and partly downwards. The younger 

 class of trees enjoy immunity from infection, because in their 

 case wounds are very quickly protected by an exudation of 

 turpentine. From the time when the heart-wood becomes 

 comparatively dry, turpentine ceases to exude from the central 

 part of a branch-wound, and this consequently becomes liable to 

 attack from the spores of the fungus. This accounts for the 



