THE CULTIVATION OF THE OAK. 157 



which germinate on the bark, but can not infect the tree 

 unless there is a wound in the neighborhood. How- 

 ever, owing to the numerous small cracks and ruptures 

 due to the injuries caused by insects, hail, frost, etc., the 

 mycelium easily gains access to the cortex and cambium, 

 and feeds on the contents of the cambium-cells, which 

 it destroys. The consequence of the irritations set up is 

 the formation of canker-like knots on the branches, and 

 the injury may be great enough to destroy smaller ones, 

 and occasionally even a large one. 



Unquestionably the most important of the diseases 

 to which the older oak-trees are subject are those which 

 result in the destruction of the timber. 



There are about six or eight of the fungi known 

 popularly as toadstools technically as Hymenomycetes 

 which are able to injure and even destroy the timber 

 of standing oaks, and while each of these pests does the 

 damage in its own peculiar way, they show considerable 

 similarity in general behavior. In the first place, these 

 fungi are unable to penetrate the bark of sound trees, 

 and their hyphae always gain access to the timber by 

 means of actual wounds and exposed surfaces of wood, 

 such as the cracks caused by frost or by the bending 

 down of heavy branches under the weight of a load of 

 snow, or the ruptured ends of broken branches blown off 

 by strong gales or struck by falling trees, or places where 

 animals have removed the bark, where cart-wheels have 

 abraded the larger roots, and so on. Once inside, the 

 hyphae of these fungi pierce the vessels, cells, etc., of the 



