Abstract
A DISEASE of vine-leaves, characterised by the presence of brown or blackish blotches, which frequently spread over the entire surface of the leaf, has been known in European and American vine-growing districts under various provincial names for some years. This disease, known in France as brunissure, was investigated by Viala and Sauvageau, who concluded that it was due to the presence of a parasitic organism to which the name Plasmodiophora vitis was given. Prof. Debray's researches show that brunissure is far more generally distributed than was hitherto suspected, having been detected by this observer in plants belonging to forty-two natural orders. In like manner, the leaf is not the part most frequently attacked, as supposed by Viala, but root, branch, flower, and in fact every portion of a plant is liable to attack. Owing to the absence of spore-formation, zoospores, nuclei, and slender pseudopodia, coupled with the fact that, although a parasite, there is no trace of malformation of the host, Debray considers that the organism under consideration cannot be included in the Plasmodiophoræ, nor in any other recognised family, and proposes for its reception a new family, Pseudocommideæ, and a new genus, Pseudocommis, allied to Vampyrellæ and Myxomycetæ. The supposed organism when in plant cells is difficult to distinguish from the protoplasm of the cell, and more especially the nucleus; it is, however, more refringent, and usually remains intact after the protoplasm has been destroyed by the use of eau de Javelle. Iodine-green and methylene-blue give a green and blue stain respectively; the most certain reaction, however, is said to be chlor-iodide of zinc, which gives a yellow or brown colouration to the plasmodia. The organism is met with under various forms in the cells of the host, never occurring in the intercellular spaces; the plasmodium may be intimately mixed with, and almost indistinguishable from the protoplasm of the cell, or distinct from the cell-contents and densely vacuolate, or finally, in assuming a spherical form, perfectly homogeneous, or with a few spherical vacuoles. Under certain conditions the plasmodium travels from the interior of the cells of the leaf or other part of the plant to the surface, where it appears as a slimy or gummy secretion, and by this means passes on to other parts of the plant which are attacked. Sometimes the external plasmodium becomes hardened into wax-like masses or cysts, which are considered to represent a resting-stage. The appearance and spread of the disease is much influenced by meteorological conditions, a sudden chill favouring its development. No preventive based on experiment is given, but it is suggested that badly diseased parts should be removed, and the external migration of the parasite checked by a dusting of powdered lime.
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A Destructive Plant Parasite. Nature 53, 18 (1895). https://doi.org/10.1038/053018a0
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DOI: https://doi.org/10.1038/053018a0