THE CULTIVATION OF THE OAK. 



161 



fungus are able to infect oak planks, beams, etc. ; and 

 the mycelium rapidly spreads on and in the wood, de- 

 stroying the cell-walls, and causing the wood to shrink 

 and crack and warp, and finally to fall to pieces. Thor- 

 ough ventilation is fatal to the fungus and stops the rot. 



FIG. 45. Oak wood destroyed by Polyporus dryadeus, showing the very 

 characteristic markings, like insect tunnels in a deep red brown ma- 

 trix. (K. Hartig.) 



A series of enemies to the oak-tree not yet referred 

 to are various gall-insects, so called because they pierce 

 the young leaves or buds, etc., 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 



