1077. Plants are subject to numerous diseases, the origin of the greater part of which is almost wholly unknown. Some, it is probable, arise from a derangement of the circulation of the fluids; and others, from an undue absorption of water. Tabes, or Gangrene, is a term applied to a general languor of the system, under which the plant withers away, or becomes rotten. In succulent plants, this or a similar disease is denominated Anasarca, or Dropsy. Scorching, or Insulation, is produced by too high a temperature ; or, by excessive evaporation. A variety of this disease is termed Marcor, or Welting. Chlorosis, or Etiolation, is a kind of constitutional debility, supposed to depend on the too great accumulation of oxygen, from the absence of light, and from other causes. It is often produced from the action of insects on the roots. Canker, or Caries, exhibits itself in small brown dead spots, which extend on all sides of a branch until they surround and kill it. The disease is continued by grafting, and no cure for it is yet known. Carcinoma is a term given to the appearance of an unusual deposit of the cambium or returning sap between the wood and the bark; in this case, the cambium becomes putrid, and oozing out through the bark, the latter separates from the alburnum, and the intervening space forms a nidus for insects, which soon destroy the tree. Extravasation, or Gumming, is one of the most common diseases of trees, and is known to most gardeners. Galls are tumid excrescences, caused by the punctures of insects. Alburnitus is a term applied to the appearance of a layer of soft wood, between layers of a wood of a harder texture, and is supposed to arise from a wet season. Albugo, Ferrugo, and Uredo, that is, mildew, rust, smut, brand, and blight, &c., are caused by the presence of innumerable minute funguses, which are to plants what intestinal worms are to animals. Ergot, or Clavus, is a brown or black excrescence from the seeds of grasses, not depending on a parasitical fungus. The ergot of rye is used in medicine. Spotting, or Necrosis, consists of small black spots on the leaves and soft parts of plants, most probably arising from wet and cold; since it is most common among exotics in cold seasons. Melligo and Salsugo are natural exudations of the juices of certain plants ; the former produces the manna of the ash ; and the latter, a saline secretion of the same kind. The names of a number of other diseases might be given; such as suffocatio, or choking up; icterus, or jaundice; pernio, or chilblain wounds caused by frosts ; exostosis, or clubbing of the roots ; crispatura, or curling, &c.; but, as no cure can be offered for them, and as, like all the preceding diseases, they are only to be prevented by regimen, their enumeration here would be of little service to the young gardener.
