tubes of a cellulose-like substance, filled with the living protoplasms of the fungus, and possess the remarkable property of being able to bore their way through or between the cellulose walls of the roots. The fungus attacks the plant about the second year, and it is not difficult to find true root-hairs on the young root-system when the apices are still free from the fungus mycelium. The parts of the root attacked alter their form slightly; they grow more slowly in length, and assume a fleshy, coral-like appearance (Fig. 7, m). Such a fungus-clothed root is called a mycorhiza, and the view is gaining ground that the symbiosis between the fungus and the root is of advantage to the oak. It has even been suggested that the mycelium performs the functions of root-hairs to the root, absorbing water and nutritive materials from the soil and passing them on to the oak, in return for a certain small proportion of organic substance which the latter can well afford. At any rate, it may be that the fungus hurries the decomposition of vegetable remains in such a way that they become available to the root sooner than would otherwise be the case. The systematic position of these remarkable fungi is not yet ascertained, but there is some evidence for the view that the mycelium is that of a truffle, though the question is still an open one.
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THE TREE—ITS ROOT-SYSTEM.