The rot, so general in growing larch, though sometimes originating in the bulb or lower part of the stem, seems to have its commencement most frequently in the roots. Thence the corruption proceeds upwards along the connecting tubes or fibres into the bulb, and gradually mounts the stem, which, when much diseased, swells considerably for a few feet above the ground, evidently from the new layers of sap-wood forming thicker to afford necessary space for the fluids to pass upward and downward—the matured wood through which there is no circulation approaching at this place within one or two annual layers of the outside. In a majority of cases, the rot commences in the roots which have struck down deepest into the earth, especially those under the stool; these having been thrown to a considerable depth by the young plant, as the tree enlarges, are shut out from aëration, &c. by the {80} superior increasing stool and hard-pressed earth underneath it; this earth at the same time becoming exhausted of the particular pabulum of the plant. It is, therefore, quite probable, from these parts of the roots being the weakest, that they will be most susceptible of injury from being soaked in stagnant water in the flat tills[19], starved during droughts in light sand, tainted by the putrid vapours of rich vegetable mould, or poisoned by the corrosive action of pernicious minerals. It may also be supposed that these smothered sickly roots, not possessing sufficient power or means of suction (endosmose), will be left out in the general economy of vegetation of the plant, thence lose vitality, and become corrupt. But this affords no explanation why the larch roots, under these circumstances, are more liable to corruption than those of other trees, or how the bulb itself should become contaminated. {81} We have cut off the top, where the diameter of the section was about three inches, from sound young larch trees, and found a similar rot proceed downwards in a few months from the section, as rises from the diseased roots in improper soil. There is something favourable to the quick progress of this rot in the motion of the sap, or vitality of the tree; as, under no common circumstances, would the wood of a cut larch tree become tainted in so short a time. The rot, though most general in trees which are chilled in wet cold tills, or starved in dry sand, or sickly from any other cause, is also often found to take place in the most luxuriant growing plants in open situations, branched to the ground, and growing in deep soil free from stagnating water. There must, therefore, be some constitutional tendency to corruption in the larch, which is excited by a combination of circumstances; and we must limit our knowledge for the present to the fact, that certain soils, perhaps slightly modified by other circumstances, produce sound, and others unsound larch, without admitting any general influence from altitude, excepting in so far as its antiseptic influence may go.