Tree Mycorrhiza

Summary The association with a mycorrhizal fungus commences, in the case of birch, while the seedling is very young, almost immediately after germination, and it exhibits no indication of injury, accruing from the fact that the whole of its root system immediately developes mycorrhiza. The whole of the water absorbed by such a seedling must pass through the mantle. It contains dissolved colloid substances from the surrounding matrix. Water is readily absorbed and readily yielded by the mantle. Roots of woodland trees, oak and beech, for example, creep over the surface of the soil, where there is an abundance of moss, and entering the lower layers of the moss carpet develop mycorrhiza. A chemotoxic action is apparently set up within the decaying moss. There are indications that in cases of severe drought when much mycorrhiza has been destroyed, certain trees, notably, birches of all sizes, and hornbeam stools, lose vitality and become specially subject to attacks from microfungi such as Melanconis stilbostoma (Fr.) Tul. and Pseudovalsa lanciformis (Fr.) Ces. and de Not. (5). I am much indebted to Dr Somerville Hastings for the photographs of mycorrhiza in situ and to the Essex Field Club for the loan of two blocks.