ix.] HEALING OF WOUNDS BY OCCLUSION. 223 



damp surface. Although this is not an absolute safe- 

 guard against the attacks of fungi simply because 

 the germinal tubes from spores can find their way 

 through small cracks at the margin of the wound, &c. 

 still it reduces the danger to a minimum, and it is 

 certain that valuable old trees have been preserved in 

 this way. 



Before passing to treat of the chief diseases known 

 to start from such wounds as the above, it should be 

 remarked that it is not inevitable that the exposed 

 surface becomes attacked by fungi capable of entering 

 the timber. It happens not unfrequently that a good 

 closure is effected over the cut base of a small branch 

 in a few years, and that the timber of the base is 

 sound everywhere but at the surface : this happy 

 result may sometimes be attained in pines and other 

 Conifers, for instance, by the exudation of resin or its 

 infiltration into the wood ; but in rarer cases it occurs 

 even in non-resinous trees, and recent investigations 

 go to show that the wood formed in these healing pro- 

 cesses possesses the properties of true heart-wood. 

 At the same time there is always danger, as stated, 

 and we will now proceed to give a brief account of the 

 chief classes of diseases to which such wounds render 

 the tree liable. 



The first and most common action is the decay 



