On some new or little-known Diseases of Plants, caused by Fungi

With these observations every one must agree, and we feel it needless to insist .upon the utility of attention to this subject by those whose opportunities and scientific acquirements may render them .competent to employ the microscope in researches demanding no less a clear and scrutinizing vision than an unprejudiced and clear-seeing mind. Many diseases of plants so important in their injurious effects upon some of the most valuable of Nature’s offerings to the use or enjoyment of mankind, such as the potato and the vine, appear to be, especially, subjects of microscopical research, “since, in most cases, the presence of a parasitic organism, a fungoid growth will be found to be the cause of the disease.” And these organisms are all of microscopic size.

In cases where the diseases of plants have occurred in connexion with fungoid growths, the question whether the disease has produced the fungus or the fungus the disease, has been answered in various ways. The view which was earliest entertained, viz., that the fungus was developed simply as a product of the morbid process by spontaneous generation from the diseased parts of the plant, has, at present, but few supporters; it is opposed to the positive observations that have been made respecting the germinating power of the spores of these parasites, as well as with respect to their persistent vitality, inasmuch as it has been proved by experiment (in the spores of Botrytis bassiana), that they will retain their vitality, in the dry state, for years together. But since the development of the fungus cannot be regarded as the direct product of the disease, the next thing is to inquire whether it has any dependent relation to the disease in another way. It has been assumed that the appearance of the fungus is always preceded by a morbid affection of the plant or of its parts, by which a fitting soil was provided for the growth of the fungus; and it cannot he denied that there are a vast number of fungi growing either upon plants entirely dead, or upon parts of them in a state of disease, as well as upon animal substances, and which, consequently, are not to be regarded as the cause of the disease, or of the death, but as accidental concomitants or followers of it. Thus, for instance, in potatoes rotten in consequence of the potato-disease, numerous forms of fungi grow, of which more than a dozen are known, but to none of which can the potato-disease be attributed.

It is equally certain, however, that even the sound organisms of plants and animals may be attacked by parasites from both kingdoms, whose presence is followed sometimes only by local morbid processes and manifold malformations, but sometimes, also, by general disease and death. To parasites from the animal kingdom it is needless here to advert; and with respect to parasitic plants, it may be remarked that some belong to the higher orders of the vegetable kingdom, as, for instance, the various species of Orobanche, the misletoe, Cuscuta, &c; but the majority of the parasites belonging to this kingdom, exist in the multitudinous class of fungi. Of plants of this kind, infesting living animals, Robin (Hist. Nat. de Végétaux parasites qui croissent sur l’homme, et les animaux vivants) enumerates not less than 86 species. To the fungi which vegetate upon living plants, belong, in the first place, the whole host of ‘rust ‘and ‘smut ‘fungi (Uredo, Puccinia, Phragmidium, Æcidium, and the allied genera) which, as ‘entophytes,’ are developed in the interior of the tissues; to these, moreover, belongs the well-known “ergot,” whose previously enigmatical nature has lately been cleared up by M. Tulasne; who, by a lengthened series of the most profound observations, has shown that the body of the ergot, which is, externally, of a blackish colour, and internally white, and which has been described as Sclerotium clavus, is only the vegetative rudiment of a claviform fungus, which is not developed until it has fallen to the earth. This fungus is very closely allied to the Sphœriœ growing upon caterpillars, and is described by M. Tulasne under the name of Claviceps purpurea. The destructive fungus of the vine-disease, the so-termed Oidium tuckeri, is certainly nothing else than a kind of mildew; and in the instance of this fungus, it has been placed beyond all doubt by numerous researches, and particularly by those of Mohl, that it originates in perfectly sound parts of the vine, the disease and death of the cuticle, with their injurious consequences upon the ripening of the fruit, not commencing till after the fungus has made its appearance. The infection of the potato-plant by the Botrytis (Peronostoma) infestans, has the greatest analogy with the vine-disease; the brown spots are the invariable sequel of the appearance of this fungus. So soon as these spots are perceived, the delicate fungoid growth must be sought for around their margins, as it rapidly disappears from the centre of them. The circumstance that the brown spots remain, although the vegetation of the Botrytis subsequently disappears, or is, occasionally, so interrupted that its presence is not readily to be detected, has given rise to the erroneous views with respect to the primary origin of the brown spots.

The morbid phenomena produced by fungi are either local or, as it may be termed, general. The former is the case with most of the fungi known under the name of ‘rust,’ when they do not exist in too great quantity, such as Trichobasis (formerly Uredo), Rubigo vera, and lineœris, Puccinia, Cystopus, Syc. These genera, however, and others, which, when existing in small quantities, have merely a local effect, when more extensively developed may exert a pernicious influence upon the entire organism of the plant or tree, by causing the falling off of the leaves, &c. This local influence, however, when it affects the blossom or its essential parts, will, of course, be followed by sterility; and in this situation the attacks of the parasite are often indicated by monstrosities in the flower or its parts ; sometimes, again, sterility is caused by the effect of the fungus being shown in the prevention of the formation of the blossom, as in the case of Euphorbia cyparissias when attacked by Æcidium Euphorbia, or even by Puccinia Euphorbia, whilst Uredo Euphorbiœ, on the other hand, induces neither sterility nor any other striking change in the plant.

When the array of diseases produced by fungi, which, formerly unnoticed, have, in later times, attracted universal attention by their destructive consequences, is surveyed, it might readily be supposed that, as in the diseases to which the human frame is subject, every period has its prevailing character, so, also, in the vegetable kingdom, certain variable and secular influences prevail, to which is to be ascribed the circumstance of the present activity of diseases produced by fungi. At any rate, it appears that the meteorological conditions in the last few years have not been so unusual that a sufficient explanation of the destructive outbreak of these diseases is to be sought for in them. Besides the formidable potato-disease, numerous other diseases belonging to the same category have, of late years, invaded the vegetable kingdom, among which is to be enumerated, as of the greatest importance, the vine-disease, whose increasing extent may be traced from year to year. In 1852, the mulberry trees in Italy were attacked by a disease previously unobserved, the cause of which was discovered by Montagne in a. fungus which invades the leaves, and is described by him under the name of Fusis-porium cingulatum. In 1851, a disease very destructive to the orange trees, was described by Rendu, as caused by the attack of a fungus upon the roots, a species of Rhizoctonium. In the summer of 1851, the different species of Ribes, in the neighbourhood of Bercelli, in Piedmont, were invaded by a fungus named Nematogonium byssinum, and whose effects were very fatal to the plants. Diseases in a similar way, produced by fungi, and invading the cultivated Parsnip, and also observed upon Pimpinella saxífraga, and upon Anthriscus sylvestris and Angelica sylvestris, have been described. The author concludes by describing and figuring several new species of fungus, one of which attacks the species of Robinia, —Septosporium curvatum; another, Acrosporium cerasi, invading the Cherry; Hemphylium, ericoctonum, a disease of the species of Erica ; and Heirochœte malvarum, one affecting the mallow tribe.