Fungi: Their Nature and Uses

by M. C. Cooke

There is one phase of the influences of fungi on the lower animals which must not be wholly passed over, and that is the relation which they bear to some of the insect tribes in furnishing them with food. It is especially the case with the Coleoptera that many species seem to be entirely dependent on fungi for existence, since they are found in no other situations. Beetle-hunters tell us that old Polyporei, and similar fungi of a corky or woody nature, are always sought after for certain species which they seek in vain elsewhere,[W] and those who possess herbaria know how destructive certain minute members of the animal kingdom are to their choicest specimens, against whose depredations even poison is sometimes unavailing.

Some of the Uredines, as Trichobasis suaveolens and Coleosporium sonchi, are generally accompanied by a little orange larva which preys upon the fungus; and in the United States Dr. Bolles informs us that some species of Æcidium are so constantly infested with this red larva that it is scarcely possible to get a good specimen, or to keep it from its sworn enemy. Minute Anguillidæ revel in tufts of mould, and fleshy Agarics, as they pass into decay, become colonies of insect life. Small Lepidoptera, belonging to the Tineina, appear to have a liking for such Polyporei as P. sulfureus when it becomes dry and hard, or P. squamosus when it has attained a similar condition. Acari and Psocidæ attack dried fungi of all kinds, and speedily reduce them to an unrecognizable powder.

III. What are the influences exerted by fungi on other plants? This is a broad subject, but withal an important one, since these influences act indirectly on man as well as on the lower animals. On man, inasmuch as it interferes with the vegetable portion of his food, either by checking its production or depreciating its quality. On the lower animals, since by this means not only is their natural food deteriorated or diminished, but through it injurious effects are liable to be produced by the introduction of minute fungi into the system. These remarks apply mainly to fungi which are parasitic on living plants. On the other hand, the influence of fungi must not be lost sight of as the scavengers of nature when dealing with dead and decaying vegetable matter. Therefore, as in other instances, we have here also good and bad influences intermingled, so that it cannot be said that they are wholly evil, or unmixed good.

Wherever we encounter decaying vegetable matter we meet with fungi, living upon and at the expense of decay, appropriating the changed elements of previous vegetable life to the support of a new generation, and hastening disintegration and assimilation with the soil. No one can have observed the mycelium of fungi at work on old stumps, twigs, and decayed wood, without being struck with the rapidity and certainty with which disintegration is being carried on. The gardener casts on one side, in a pile as rubbish, twigs and cuttings from his trees, which are useless to him, but which have all derived much from the soil on which they flourished. Shortly fungi make their appearance in species almost innumerable, sending their subtle threads of mycelium deep into the tissues of the woody substance, and the whole mass teems with new life. In this metamorphosis as the fungi flourish so the twigs decay, for the new life is supported at the expense of the old, and together the destroyers and their victims return as useful constituents to the soil from whence they were derived, and form fresh pabulum for a succeeding season of green leaves and sweet flowers. In woods and forests we can even more readily appreciate the good offices of fungi in accelerating the decay of fallen leaves and twigs which surround the base of the parent trees. In such places Nature is left absolutely to her own resources, and what man would accomplish in his carefully attended gardens and shrubberies must here be done without his aid. What we call decay is merely change; change of form, change of relationship, change of composition; and all these changes are effected by various combined agencies—water, air, light, heat, these furnishing new and suitable conditions for the development of a new race of vegetables. These, by their vigorous growth, continue what water and oxygen, stimulated by light and heat, had begun, and as they flourish for a brief season on the fallen glories of the past summer, make preparation for the coming spring.

Unfortunately this destructive power of fungi over vegetable tissues is too often exemplified in a manner which man does not approve. The dry rot is a name which has been given to the ravages of more than one species of fungus which flourishes at the expense of the timber it destroys. One of these forms of dry rot fungus is Merulius lacrymans, which is sometimes spoken of as if it were the only one, though perhaps the most destructive in houses. Another is Polyporus hybridus, which attacks oak-built vessels;[X] and these are not the only ones which are capable of mischief. It appears that the dry rot fungus acts indirectly on the wood, whose cells are saturated with its juice, and in consequence lose their lignine and cellulose, though their walls suffer no corrosion. The different forms of decay in wood are accompanied by fungi, which either completely destroy the tissue, or alter its nature so much by the abstraction of the cellulose and lignine, that it becomes loose and friable. Thus fungi induce the rapid destruction of decaying wood. These are the conclusions determined by Schacht, in his memoir on the subject.[Y]

We may allude, in passing, to another phase of destructiveness in the mycelium of fungi, which traverse the soil and interfere most injuriously with the growth of shrubs and trees. The reader of journals devoted to horticulture will not fail to notice the constant appeals for advice to stop the work of fungi in the soil, which sometimes threatens vines, at others conifers, and at others rhododendrons. Dead leaves, and other vegetable substances, not thoroughly and completely decayed, are almost sure to introduce this unwelcome element.

Living plants suffer considerably from the predations of parasitic species, and foremost amongst these in importance are those which attack the cereals. The corn mildew and its accompanying rust are cosmopolitan, as far as we know, wherever corn is cultivated, whether in Australia or on the slopes of the Himalayas. The same may also be said of smut, for Ustilago is as common in Asia and America as in Europe. We have seen it on numerous grasses as well as on barley from the Punjab, and a species different from Ustilago maydis on the male florets of maize from the same locality. In addition to this, we learn that in 1870 one form made its appearance on rice. It was described as constituting in some of the infested grains a whitish, gummy, interlaced, ill-defined, thread-like mycelium, growing at the expense of the tissues of the affected organs, and at last becoming converted into a more or less coherent mass of spores, of a dirty green colour, on the exterior of the deformed grains. Beneath the outer coating the aggregated spores are of a bright orange red; the central portion has a vesicular appearance, and is white in colour.[Z] It is difficult to determine from the description what this so-called Ustilago may be, which was said to have affected a considerable portion of the standing rice crop in the vicinity of Diamond Harbour.

Bunt is another pest (Tilletia caries) which occupies the whole farinaceous portion of the grains of wheat. Since dressing the seed wheat has been so widely adopted in this country, this pest has been of comparatively little trouble. Sorghum and the small millets, in countries where these are cultivated for food, are liable to attacks from allied parasites. Ergot attacks wheat and rice as well as rye, but not to such an extent as to have any important influence upon the crop. Two or three other species of fungi are sometimes locally troublesome, as Dilophospora graminis, and Septoria nodorum on wheat, but not to any considerable extent. In countries where maize is extensively grown it has not only its own species of mildew (Puccinia), but also one of the most enormous and destructive species of Ustilago.

A singular parasite on grasses was found by Cesati in Italy, in 1850, infesting the glumes of Andropogon.[a] It received the name of Cerebella Andropogonis, but it never appears to have increased and spread to such an extent as was at first feared.

Even more destructive than any of these is the potato disease[] (Peronospora infestans), which is, unfortunately, too well known to need description. This disease was at one time attributed to various causes, but long since its ascertained source has been acknowledged to be a species of white mould, which also attacks tomatoes, but less vigorously. De Bary has given considerable attention to this disease, and his opinions are clearly detailed in his memoir on Peronospora, as well as in his special pamphlet on the potato disease.[c] One sees the cause of the epidemic, he says, in the diseased state of the potato itself, produced either accidentally by unfavourable conditions of soil and atmosphere, or by a depravation that the plant has experienced in its culture. According to these opinions, the vegetation of the parasite would be purely accidental, the disease would be independent of it, the parasite would be able frequently even to spare the diseased organs. Others see in the vegetation of the Peronospora the immediate or indirect cause of the various symptoms of the disease; either that the parasite invades the stalks of the potato, and in destroying them, or, so to speak, in poisoning them, determines a diseased state of the tubercles, or that it introduces itself into all the organs of the plant, and that its vegetation is the immediate cause of all the symptoms of the disease that one meets with in any organ whatever. His observations rigorously proved that the opinions of the latter were those only which were well founded. All the alterations seen on examining spontaneous individuals are found when the Peronospora is sown in a nourishing plant. The most scrupulous examination demonstrates the most perfect identity between the cultivated and spontaneous individuals as much in the organization of the parasite as in the alteration of the plant that nourishes it. In the experiments that he had made he affirms that he never observed an individual or unhealthy predisposition of the nourishing plant. It appeared to him, on the contrary, that the more the plant was healthy, the more the mould prospered.