TUE CULTIVATION OF THE OAK 161 
the mycelium rapidly spreads on and in the wood, 
destroying the cell-walls, and causing the wood to shrink 
and crack and warp, and finally to fall to pieces. 
Thorough ventilation is fatal to the fungus and stops 
the rot. 
A series of enemies to the oak-tree not yet referred 
Fie, 45.—Oak wood destroyed by Polyporus dryadeus, 
showing the very characteristic markings, like insect 
tunnels in a deep red-brown matrix. (R. Hartig.) 
to are various gall-insects, so called because they pierce 
the young leaves or buds, &c., and lay their eggs in the 
wound ; the irritation set up suffices to induce a flow of 
food materials to the stimulated spot, and the overfed 
M 
