I put together in one artificial class a varied group of diseases, the principal symptom of which is the escape of fluids from the tissues, under circumstances which betray an abnormal state of affairs, often obvious, but sometimes only to be inferred. In many of these cases bacteria abound in the putrefying mass, and some evidence exists for connecting these microbes causally with the disease in a few of the more thoroughly investigated cases, but in no case has this been sufficiently demonstrated; and considering the ease with which bacteria gain access via wounds caused by insects and fungi, as well as by other agents, the necessity for rigid proof must be insisted upon before we can accept such alleged examples of Bacteriosis.
Damping off. - When seedlings are too closely crowded in beds kept too damp, or in moist weather, they are very apt to rot away, with all the symptoms spreading from a centre, contagious infection, mycelia on and in the tissues, etc. - of a fungus attack. The commonest agent concerned is one of the species of Pythium, the propagation of which is favoured by the rank, over-turgid, and etiolated conditions of the plants. Species of Mucor, Botrytis, and other fungi, may also be met with.
Cuckoo-spit. - The leaves of Willows, Meadow grasses and herbs, etc., are often seen with froth on them, in which is a green insect, Aphrophora, which sucks the juices from the tissues and excretes the frothy watery cuckoo-spit from its body.
The rotting of bulbs, roots, etc., has been much discussed during the last few years in the pages of the Gardeners' Chronicle, Zeitschrift fur 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 Ange-blich durch Bakterien verursacht werden, Semarang, 1892.
The most convincing accounts, however, are since that date; see Smith, "Pseudomonas Campestris," Cent.f. Bakt., B. III., 1897, p. 284, and Arthur and Bolley, Bacteriosis of Carnations, Perdue University Agr. Expt. Station, 1896, Vol. VII., p. 17. Woods has lately shown that this disease is due to Aphides only, the bacteria having nothing to do with the disease primarily, Stigmonose, Bull. 19, U.S. Dept.
Agr., 1900; but it is necessary to bear in mind that actual penetration of the cell-walls from without must be proved, as De Bary proved it for germ-tubes of fungi, before the evidence that Bacteria are truly parasitic in living plants can be called decisive. This is a difficult matter, but until it is settled we do not know whether these organisms are really parasitic in the sense that Phytophthora is, or merely gain access by other means - I have traced them through dead fungus - hyphae - to the vessels, dead cell-walls, etc. The proof of infection via water pores and vessels is given for one species by Harding, "Die Schwarze Faulnis der Kohls," etc., Cent. f. Bakt., Abh. II., B. VI., 1900, p. 305, with literature.
Concerning the "Damping off" of seedlings, see Marshall Ward, "Observations on the Genus Pythium," Quart. Journ. Microsc. Soc., Vol. XXIII., 1883, p. 485, and Atkinson, Bull. 94 of Cornell University Agric. Expt. Station, 1895, P. 233.
On Bacteriosis in Turnips, see Potter, Proc. R.S. 1901, Vol. LXVII., p. 442.