Page:The Oak.djvu/171

 wood-pigeons and other birds. In the north of Europe the young plants suffer terribly from the ravages of a fungus named Rosellinia, the mycelium of which sends its branches into the roots and kills them, consequently entailing the death of the plant. The larvae of various insects also damage the roots and bring about injuries which may prove fatal. Cynips corticalis produces galls on the lower parts of the stems.

When the plant has passed into the condition of a sapling its dangers are for the most part of quite other nature, the injurious fungi especially being different. The chief diseases of the roots now arise from their spreading into unsuitable soil, the drainage of which may be incomplete, and thus bring about a sodden, acid, ill-aerated condition. The want of oxygen and the low temperature combine to kill the root-hairs and young rootlets, and the leaves above part with their water faster than it can be supplied from below, and they turn yellow and die off, the branches dry up, and the tree dies.

Other dangers arise from the persistent overshadowing of other trees, which slowly kill the young oaks by depriving their leaves of light; the offending trees playing the same inimical part, in fact, that grass and weeds, etc., play towards the small seedlings. Or the roots may be too thickly set in the soil if the trees are too crowded, and each suffers from over-competition with others.

Much mischief is effected by the attacks of insects