Page:The Oak.djvu/179

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

Fig. 45.—Oak wood destroyed by Polyporus dryadeus, showing the very characteristic markings, like insect tunnels in a deep red brown matrix. (R. 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