Tubers are often found with the cork burst and peeling in shreds, the flesh more or less converted into a putrid and stinking pulp, with a spotted brown boundary of partly destroyed but firmer tissue between the dark utterly rotten and the white and still firm healthy flesh. The principal agent in the destruction of the tissues is _Clostridium_, an anaerobic bacillus which consumes the cell-walls but leaves the starch intact. Hence a thoroughly decomposed tuber consists of a cork bag full of starch and foetid liquid. In the dried condition the flesh shows a brown marbling; this passes into a soft soupy starchy part, and here and there may be violet grey cavities lined with _Spicaria_, _Hypomyces_, etc., the white stromata of the latter often appearing externally. The excavations are filled with loose starch grains, and bounded by cork and cambium formed in the peripheral cells. The cell-walls eventually undergo slimy decomposition. _Spicaria_, _Fusisporium_, various moulds, and bacteria may all be associated with wet-rot. Dry-rot of Potatoes is also due to various fungi and bacteria, but the destructive action goes on slowly, owing to there being no more moisture than the tissues afford. The flesh becomes excavated here and there, owing to the slow destruction of the cell-walls by _Clostridium_: the destroyed tissues are brown, and the uninjured starch grains powder them all over. Finally the whole shrunken mass has a crumbly consistency. When the flesh remains white, but assumes a powdery consistency and dry-rot, with the cork destroyed here and there, Frank refers the damage to _Phellomyces_. Where the dry-rot is due to _Fusarium_ the chalk-white stromata may often be detected breaking through the periderm; but it must be remembered that the soil-contaminated, broken skin of a potato-tuber is a favourable lurking spot for many fungi, and _Periola_, _Acrostalagmus_, and others have been detected therein. Brown spots, depressed into the flesh, sometimes result from the ravages of _Tylenchus_, the minute worms being found in the diseased tissues. In some cases the flesh turns watery and soft, grey, almost glass-like, starting at the haulm end, and this may be owing to the invasion of _Rhizoctonia_. NOTES TO CHAPTER XXV. The rotting of bulbs, roots, etc., has been much discussed during the last few years in the pages of the _Gardeners' Chronicle_, _Zeitschrift für Pflanzenkh._, and elsewhere. The principal references to Bacteriosis--the rot in which bacteria are stated to be the primary agent causing these and similar diseases--may be found in Massee, _Diseases of Plants_, pp. 338-342, and more fully in Russell, _Bacteria in their Relation to Vegetable Tissue_, Baltimore, 1892; and in Migula, _Kritische Uebersicht derjenigen Pflanzen-krankheiten, welche Angeblich durch Bakterien verursacht werden_, Semarang, 1892.