The Parents' Review

A Monthly Magazine of Home-Training and Culture

The Seasons
"Knowledge Never Learned of Schools."

Tree Destroying Fungi.

By Mrs. Dorman.

One is apt to indulge in feelings of resentment against those members of the vegetable kingdom who support themselves by no honest work of their own, but simply appropriate to their service the nutrient substances formed by the ordinary hard-working individuals of the community. It seems hard that the apple tree should be robbed of its juices by the parasitic misletoe, or that the wild thyme or flax should be strangled by the dodder that has nourished itself at their expense. So profitable does a certain parasitic plant of Sumatra (Rafflesia Arnoldi) find this mode of life that it can produce the largest flowers of any known plant. This gigantic robber, whose first discovered flower was nine feet in circumference and weighed fifteen pounds, held twelve pints of fluid in its cup. These three parasites may and do exhaust their victims, but do not actually promote disease. Very different is it with such as Oidium Tuckeri, the vine-mildew, and the other microscopic fungi that cause rust and smut and ergot in our cereal crops, for flowering parasites are, as a rule, far less injurious than cryptogamic. The more minute the enemy as an individual the more are his ravages to be dreaded collectively; man can protect himself without much difficulty from beasts of prey, but in the presence of an invading army of ants he is powerless, and can only wait till they take themselves off.

It was a long point of discussion as to whether fungi were the cause, or only the accompaniment of disease in plants, but it has been decided in favour of the former alternative, because it has not only been proved that the same fungus always accompanies the same disease, but it has been shown by experiment that these diseases are contagious, and may be induced by sewing the spores of the particular fungus upon a healthy plant. The higher orders of vegetation appeared in the first instance upon the débris of vegetation of a lower order, such as algae, fungi, lichens and mosse; but as Figuier remarks, when plants of a superior order are struck by death they become a prey to the humbler thallogens, and sometimes even during their life these parasite attach themselves to them and ultimately destroy them, as in the case of the Tree-destroying Fungi. To produce and to destroy is, he says, the double mission of thallogens, but on two conditions--an evanescent and short existence, and to multiply themselves to infinity and with great rapidity. Some mushrooms are said to produce 600,000 cells a minute. So rapidly do the more conspicious fungi appear and disappear under the favourable conditions of autumn, that many persons suppose they are peculiar to that season, but in fact they are developed all the year round. For the greater part of the year perhaps, their life is a hidden life, but unceasingly they are preying in secret upon the tissues of some living victim, or hastening the dissolution of an already decaying organism, and their presence is manifested by the rapid and sudden development of the receptacle, the most conspicuous part of a fungus. In the case of trees, the so-called mycelium penetrates the wood-cells, softens and disintegrates them, thus producing disease, and ultimately death. The vegetative body of a fungus consists of a number of very fine interlacing filaments or hyphae, which are commonly entirely buried in the tissues of its host or of some organic substratum. These filaments pierce the membranes of other cells in order to live on them and in them, and the reason is apparent when we consider the entire absence of chlorophyll in fungi, for as they cannot build up organic compounds they must obtain them ready-made. They cannot derive carbon direct from the carbon-dioxide of the atmosphere, but are dependent on substances already organized, consequently all fungi are either parasites upon other plants or animals, or are saprophytes on decaying organic matter. On germinating, the spore of a fungus gives rise to the mycelium or spawn, which buries itself in the tissues of its host, and from it rises into the air a body composed of densely packed hyphae known as the receptacle. Everyone is familiar with the receptacle of the common mushroom; with its stout stem supporting the cap or pileus under which appear the pink or brown characteristic gills, upon which are formed the spores; but the Polyporei, the most deadly enemies of trees, instead of gills, have the under surface of the hymenium perforated by myriads of little holes. If the hymenium be divided into two halves, it will be seen that the flesh of the cap is thick and solid, and that the under part is composed of slender tubes closely packed side by side, and their mouths corresponding to the holes covering the surface. The spores are formed within the pores.

These fungi are often hard and woody; they have a very short stem, usually on one side of the hymenium, and may be seen growing in dense layers on the stumps of old trees. Polyperus sulphureus is a common fungus on the trunks of trees such as poplars, beeches and willows. P. ignearius is another, and P. dryadeus is the special enemy of the oak. Each tree has its own peculiar fungus. Polyporus betulinus grows upon birch trees, and another species on the larch; Agaricus ulmarius supports itself at the expense of the elm, and A. osreatus, or the oyster fungus, is found upon various trees. Polyporus squamosus is a familiar species upon decaying ash trees, and occasionally attains enormous dimensions, such as seven feet in circumference, with a weight of forty-two pounds. According to Dr. Greville, this size was attained in four weeks, giving an increase of growth equal to nineteen ounces per day. Another reached a diameter of eleven inches within the space of a week.

Another class of fangus is the cause of the serious disease of gangrene or canker, which so commonly attacks apple and pear trees in damp or unfavourable conditions, for it must be noted that excessive moisture is a predisposing cause in all fungoid diseases. The spores of the fungi are in this case the exciting cause of disease, but it is believed that some change is first procuced in the cells of the plant which enables the spores to find a nidus. The cellulose is first transformed into "a muddy fluid, a brown humus-like powder or a carbonaceous mass," and the disease then assumes a peculiar type, because of the presence of the fungus, often a species of Nectria. Gangrene may be moist or dry according as the product of decomposition is fluid or solid. Dry gangrene usually attacks the innermost layers f wood, and a sound appearance may be kept up outside until the disease reaches the cambium layer, when death quickly ensues. External injury is doubtless a frequent means of promoting fungoid diseases, and as noted above excessive moisture is a predisposing cause. There is a fungus called Coleosporum which is a great enemy to the leaders of pine trees, and often destroys them entirely. When timber has been felled or when stumps are left in the ground, the processes of decay and decomposition are aided by the ubiquitous fungi, and viewed under this aspect their effect is entirely beneficent, for by the disruption of the organic compounds in dead plants, their carbon and nitrogen are given back to the atmosphere for the further use of vegetable life, and if there were no putrefaction and decay, so much carbon and nitrogen would be locked up, and the earth would become so cumbered with dead organisms, that life would be rendered impossible. Schoolboys are weel acquainted with the delights of touchwood, which is caused by the mycelium of a fungus permeating the wood of an old stump, and exhibits phosphorescence in the dark. The mycelium of fungi picks timber to pieces as men pick oakum, and dry-rot is the result. Unfortunately they do not confine themselves to the disintegration of dead wood, but attack living trees and felled timber, and thus produce a dread disease called dry-rot, because it reduces its host to dust. Its cause, however, is not dryness, but excessive moisture, and Merulius lacrymans often dripping with water, though its tears do not hinder its work of destruction. Other fungi injure trees by destroying or interfering with the normal action of their leaves; of such is the coffee-leaf disease, and many others, chiefly known as mildews. Numbers of species are found in woods, but as they are chiefly nourished by decaying matter they, perhaps, are not the cause of injury to the trees.

It may be noted here that the green colour of one of the woods used in the manufacture of Tunbridge ware [inlaid woodwork] is due to the presence of the green mycelium of Helotium druginosum, which traverses the whole fabric of the wood. It attacks fallen oak branches, and is not very common. It seems curious that the mycelium should be green, and one wonders what gives it the colour since it cannot be owing to chlorophyll.

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