attacked, than the stem itself is subject to change, becoming spotted here and there with dark brown patches, in which the cells are mostly filled with a dark grumous mass, without exhibiting any mucedinous filaments; though, occasionally, I have ascertained their presence. Very rarely fructifying but dwarfed specimens of the mould occur upon it. The stem now rapidly putrefies, the cuticle and its subjacent tissue become pulpy, and separate when touched from the woody parts beneath. The whole soon dries up, and in many instances exhibits in the centre the black, irregular fungoid masses which are known under the name of _Sclerotium varium_, and which are believed to be the mycelium of certain moulds in a high state of condensation. “If the tubers are now examined, the greater part will often be found smaller than usual, especially if the disease has commenced at an early stage of growth; but in their natural condition, while here and there a tuber, particularly if it has been partially exposed, exhibits traces of disease. The surface is, however, soon marked with livid patches, commencing generally about the eyes, or at the point of connection with the fructifying shoots: these rapidly acquire a spotted appearance, the spots being rather waved, and assuming often a more or less concentric arrangement. Sometimes—especially on the smoother kinds of tuber—two or more regular systems of concentric spots are exhibited on the same tuber. The skin now withers, and is easily separated; the spots become depressed and of a yellowish tinge; and if the tubers be laid in a moist place, in a day or two—sometimes in a few hours—the same mould which destroyed the leaves springs from them, piercing the cuticle from within, yet not scattered, as on the leaves, but forming a conspicuous white tuft. If a section of the diseased tuber be made on the first symptoms of the disease, little brownish or rusty specks are found in the cellular tissue, confined, with very rare exceptions, to the space between the cuticle and the sac, if I may so call it, of spiral vessels and their accompanying tissue, which, springing from the subterranean branches, pass into the tuber, making their way to the several buds disposed on the surface. These spots consist at first of a quantity of discoloured cells, mixed more or less with others in a healthy condition. The grains of fecula are for a long time perfectly healthy; the cells themselves, so far from being looser, are more closely bound together than in the more healthy portions. The rusty spots soon exhibit a darker tint, spreading in every direction and becoming confluent; they at length extend beyond the barrier of vascular tissue, and attack the central mass. The tuber, meanwhile, assumes a disagreeable smell, decomposes more or less rapidly, other Fungi establish themselves on the surface, or in the decaying mass, which emits a highly fetid odour, resembling that of decaying agarics; the union of the cells is