THE 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 



FIG. 45. Oak wood destroyed by I'olyporus 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 



