Popular Science Monthly/Volume 29/August 1886/Woods and their Destructive Fungi I
|WOODS AND THEIR DESTRUCTIVE FUNGI.|
IN the forests which have contributed so much to the industries and wealth of the United States there are seventy species of trees which have been and are of great commercial importance, and three hundred and forty more species which have an economic value. But few countries have so great a variety.
A section from the trunk of a tree of nearly the entire list of the species, gathered from all parts of the United States, can now be seen in the great and valuable collection in the American Museum of Natural History of New York City, contributed by Mr. Morris K. Jesup. The difficulties attending such a great work, so as to show the appearance of the wood and size of the tree with its bark, can only be fully appreciated by those actually engaged in making the collection. The magnitude of the work is without precedent; and, while it has been possible to transport across the continent a section of a tree, it has not been possible to fully protect some of them from the attacks of fungi, and some species will have to be replaced, while others by seasoning have checked the ravages of their fungi, but they show discoloration of the wood. To many this is an objection, but, by showing what species easily decay, it enhances the economic value of the collection. So many of our primitive forests have been cut, that many species for general use are already consumed, and the importance of these specimens for study, in making selections for substitutes, can not be over-estimated.
An inspection of the different species shows the marked diversity in the structure and appearance of the woods, and one is quickly relieved of the general impression that they are all alike. Examined microscopically, the differences in structure are sufficient for justification of the species, and at the same time enable one to judge of the suitability of a particular wood for definite uses. 80 little has been done in this country in the microscopical study of the woods for engineering, architectural, or mechanical purposes, that but few are aware of the variety in form and structure of the wood cells, ducts, and special fibers which make up the woody tissue of the different species. An expert can readily determine whether a certain wood, used for rail-road-ties, will sustain the service of a trunk line, or is only suitable for a branch of limited traffic.
In the Coniferæ, which includes the pines, cedars, larches, red-woods, spruces, and firs, as a rule, each layer of growth only has two kinds of wood-cells called tracheids, one of thin walls and a large lumen, and the other of thick walls and a small lumen; when the former pre-dominates, making nearly all of the layer, the wood is generally soft, as in the white pine (Pinus strobus, L.), the cedars, redwoods, spruces, and firs. When the thick-walled cells form one fourth to one half of the layer, the wood is much harder, as in the long-leaf yellow pine (Pinus palustris, Mill), Pinus mitis, and the larches. On the thin-walled
|Fig. 1.—Transverse Section of Pinus palustris (Mill), 20/1.||Fig 2.—Transverse Section of Chamæcy-paris sphœrorda (Spalch),20/1 (White Cedar).|
cells of all the species of the Coniferæ are dome-like or lenticular markings, principally on the sides parallel to the medullary rays.
The thick-walled cells are often marked on the sides at right angles to the medullary rays. The Coniferæ have more or less resinous products, and the presence or absence of the upright resin-canals aid in distinguishing the genera, while the form and character of the medullary rays, the presence or absence of resin-ducts, the character of the cells, enable the species to be identified. In the alburnum or sap-wood, the starch is confined to the cells around the resin-canals and in the cells of the medullary rays.
The cellular structure of the oaks, chestnuts, hickories, ashes, walnuts, maples., beeches, birches, and magnolias is far more complex and more highly differentiated than that of the conifers; beside the wood-cells, there are ducts, vessels, and special cells containing starch in the alburnum or sap-wood. In nearly all the species of the first five orders mentioned, the ducts grow in concentric rows, in the first of the season's growth; those which, form later may be inclined through the layer of wood-cells, becoming smaller as they approach the outer portion. In the live oak, the ducts run radially through the ring, and the small fibers are nearly solid, giving the wood great hardness, making it so valuable for ship-building.
In the maples, beeches, birches, and magnolias the ducts are well interspersed through the entire ring, and are nearly of the same size. In the alburnum of these woods there are a great many cells which are filled with starch as reserve material, like the medullary rays in this portion of the wood. During active growth the starch is transformed and withdrawn. In the duramen but little starch remains, other products taking its place.
In the hard woods, all or portions of the annular rings are made up of hard and nearly solid fibers, while in the softer woods the walls are not so thick. In many of the species each layer of growth is not
|Fig. 3.—Transverse Section of Quercus alba, 20/1.||Fig. 4.—Transverse Section of Liriodendron talipfera, Liriodendron talipfera, 20/1 (White Wood).|
of uniform thickness or quality, some having but comparatively few of the dense, hard fibers, the growth of these depending upon certain climatic conditions which may not yearly occur.
In the thick forests, under quite uniform conditions of growth, the thickness of the annular ring largely depends upon the leaf-area, which remaining practically the same in the older trees, the wood-cells forming upon a larger diameter, the rings as a rule are not so thick or dense as those grown when the tree is much younger.
Formerly, in lumbering, the trees were felled in the winter, cut into logs, sledded on the snow to the streams, and driven down in rafts in the spring to the mills. Now, with the log-railroads, they are independent of the snow, and in many camps lumbering is carried on through the entire year. In the spring of 1876 I laid out a short log railroad in the Michigan forests. The cut of the company for that year was 8,000,000 feet, board-measure; for 1886 it will be 120,000,000 feet, largely to supply the Atlantic coast with white-pine lumber.
Timber cut in the spring growth, when the starch in the sap-wood is transforming, furnishes in this part of the wood a good media for the growth of various ferments which produce decomposition in such products, and unless quickly checked will start the decay of the woody tissue.
It was the universal belief, until a few years since, and is still a common one, that the decay of timber was due to Eremacausis—slow combustion. It is to the improvement and use of the microscope and its accessories, that the true causes of decay of wood, are found to be due to various forms of fungi. Many definite forms which cause fermentation have been traced and more are known to exist which are beyond the definition of present microscopes, unless they can be stained so as to differentiate them. Photo-micrographs, which give indications of structure far beyond what the eye can recognize, are important aids in this study, while the details they give of the structure of the wood could not be obtained in any other manner.
What are the fungi?
A great group of a low order of leafless and flowerless plants, destitute of chlorophyl, many of them microscopic, whose functions are under certain conditions to break up and liberate the compounds of and in the cell-structure, formed by chlorophyl-bearing leaves in the sunlight.
In short, the functions of the growing fungi are to undo and return to the air and soil the elements assimilated by the higher plants and trees in their woody structure during growth.
A mycologist would give a different definition of the fungi having reference to the form of fructification and spores, their functions being of less importance to him; while an epicure would only describe the mushrooms which please his taste.
It is now estimated that over fifty thousand species of fungi have been described; less than five hundred of them were known in the beginning of the century. A great number of the species are confined to special habitats, and all of them will not be found upon the woods. One fungus may only be found upon one or two species of wood, while others will be more general. The species we illustrate by cuts belong to the highest orders, and are typical to some extent of many others. Associated with these are some of unicellular structure, which belong to the genus Saccharomycetes—or budding fungi—of which the yeast-plant is typical; and others belong to the Schizomycetes, the fission fungi—bacteria, etc.—forms of which are attracting so much attention in connection with diseases of mankind.
Generally speaking, the first condition by which the higher fungi —illustrated here—can be detected is by their mycelia, consisting of filaments of, usually, white cells, branching repeatedly by lateral ramifications, growing at their apices, lacing and interlacing, forming in many places dense, felted masses. When they grow on the under side of a plank, closely packed boards, and railroad-ties, they are often similar in form to that shown in Fig. 5. So far as the decay of the wood is concerned, the mycelia of the fungi is the most important part. Though these filaments are small, ranging from 0·0004 to 0·002 of an inch in diameter, they are able to pierce the walls of the wood cells when softened by moisture, which many of them seem to generate to aid in their destructive work.
The fungi, instead of propagating by visible seeds, only have microscopic spores, which are freely disseminated by the air to resting places. When proper conditions for germination occur, the spore sends out a mycelium, which, by spreading over the under side of a plank, as seen in Fig. 5, induces, sooner or later, the decomposition of the structure of its host, to partly build up its own.
Where it has once run over the wood in a dense growth, it destroys its strength from one eighth to three fourths of an inch in depth, and if the wood dries, cracks and crumbles to pieces (see Fig. 5)—it forms the so-called "dry rot" in timber, which is said to take place when the wood is perfectly dry. This is a misconception, as it is impossible for decay to commence without moisture, sufficient heat and access of air to supply the amount of oxygen needed in the reduction of the tissue to lower compounds.
If the wood does not dry, the mycelia continues to grow until all of the wood-cells are disorganized and fall to pieces, or, in other words, completely rotted. In many cases, the mycelia works in the inner portions of the timber, as explained later, and does not show exteriorly until decay is well advanced; this is especially true of larger timber.
"Dry rot" was named from the effect produced, and not the cause, to distinguish it from the so-called "wet rot." It has been an unfortunate designation, misleading many people, causing them to believe that timber will rot when dry, and proper precautions have not been taken to prevent decay, on the supposition that it would occur in any event.The illustration in Fig. 5 is that of the mycelium of the Polyporous radula (? Fr.) spreading on the under side of the plank of station platforms, which were destroyed in a year and a half to two years. It is typical of a large number of the mycelia of the fungi growing in similar conditions. One sees the same general appearance on lumber, plank, and sawed railroad-ties, which are piled together without being separated from each other by a small air-space. Hemlock inch boards can be completely rotted through in six to eight weeks of July and August weather, by the mycelia attacking both sides of the boards when damp, and piled up without an air-space between each. Cargoes
of lumber and timber in long voyages are often badly injured by the growing mycelia between the pieces.
In bridges, ends of posts and struts, tenons and mortises, there are often similar growths of mycelia arising from the germination of spores by moisture, and decay eventually takes place. The illustration presented in Fig. 5 is one quite familiar to all who handle lumber and timber, but its import is not as generally understood as it should be, from the fact that such growths are thought to be due to the decay of the wood, instead of being the inducing cause.
A little more care in piling and stacking green lumber by producers and consumers, permitting circulation of air between each piece, would prevent the growth of various mycelia, and save annually large quantities of lumber.
If moisture collects and remains on seasoned timber, the mycelia will also grow and destroy it. Large timber should be seasoned under sheds, otherwise the sun will season an outside layer, preventing the escape of moisture, and internal growths of ferments and mycelia-fungi will destroy the inside of the timber, a thin outer shell remaining sound for some time.
The illustration is one of the most important that can be presented. It shows the destruction induced by the growing mycelium on the wood. On the right and lower edges, where the growth first appeared, it has caused the wood to crack not only with the fibers, but across, and in a short time longer it would have fallen to pieces, as portions of adjacent planks had some time previously.
The form of fructification of the fungus of mycelium shown in Fig. 5, as found, was resupinate, attached to the under side of the plank as that shown in Fig. 6, which is a species of Polyporous very destructive to hemlock in inclosed warm and damp places.
Resupinate forms of the Polyporei are very common on the under side of boards and timbers they are destroying, covering irregular areas; some will be ten by four inches, others follow along the edge of a board adjacent to a wall, ten to twenty inches, having an irregular width of one to two inches, the pores always pointing downward. A definite contour not being followed, identification of the species is often very difficult.
Fig. 7 shows the under and upper sides of the fruit of the fungus Lentinus lepideus (Fr.)—"Scaly Lentinus"—an agaric, and in this immediate territory is the one so destructive to timber of yellow or Georgia pine (Pinus palustris, Mill) in bridges, docks, and railroad-ties.
I have also found it upon the timber of Pinus mitis. Being the first to call attention to its destructive influence, its brief technical description will not be out of place: "Pileus fleshy, firm, convex, or expanded, nearly white, spotted with dark brown, appressed scales; lamellæ rather broad, not crowded, attached, slightly emarginate, and decurrent, white, the edge rough, eroded or torn, stipe firm, solid, equal or
tapering downward, more or less scaly, whitish, sometimes eccentric, straight, or curved. Height, two to four inches; breadth of pileus, three to five inches; stipe, one half to three fourths of an inch thick."
Monstrous forms occur in dark situations with or without a pileus. Only a single stipe and pileus are here shown as emerging from a crevice in the wood; generally two, and sometimes four occur. The small block in Fig. 7 shows the mycelium in the longitudinal resin-ducts (see Fig. 1), which it readily pierces, hastening the destruction of the wood.
On the gills or lamellæ are borne the spores, which are 0·003 of an inch long, and 0·0013 of an inch in diameter, they are curved and one end apiculated; drop out and are carried by the wind to some resting-place; and when the proper conditions occur, germinate, sending out the mycelium, which only fruiting under very favorable conditions from June to September, the fruit is rarely found. I have seen many thousand ties in main tracks destroyed by it, without finding a specimen of the fruit; its mycelium is very abundant, and pierces the coarser cells of the wood with great rapidity, generating sufficient moisture, having an acid reaction, to carry on its destructive work, provided external heat and currents of air are not sufficient to dry the wood.
Examining many pieces of bridge-timber of Pinus palustris (Mill), which were horizontal, I found that where they had rested on others, sufficient moisture had collected to germinate the spores, and the mycelia had followed the longitudinal cells each way, meeting in the center, between the supports; the outer portions of the timber remaining dry, did not allow the moisture to escape, and the fungus was destroying the inside, while the outside looked sound. In bridge-plank the moisture accumulated where it rested on the joists, the mycelia working upward and each way, usually leaving a thin portion of one eighth to one fourth of an inch in thickness, on the under side of the plank, where exposed to the air, giving the appearance that it was all sound. The abundant fructification during a brief warm rain in September, 1883, was the first indication of the destruction which had taken place.
The upright cells or tracheids composing the annular ring of the Pinus palistris (Mill) are of two kinds—one of thin and the other of thick walls; the former fill the inner part of the ring, the latter the outer portion, giving the great strength and hardness characteristic of this wood; interspersed through the ring are a few resin-ducts. In decay induced by its special fungus, the mycelium often separates some of the annual layers, and in most cases the thin-walled cells are first softened. Driving spikes into railroad-ties of this wood breaks and loosens the layers, and facilitates the entrance of the mycelium, and then larvae, from one sixteenth to one eighth of an inch in length, eat and bore in the large softened tracheids, leaving the harder ones, so that in ties of four to seven years' service we often find little more than a series of nearly separated shells. The mycelium of this fungus once in a road-bed lives for some time, and in summer is ready to attack new ties of this timber as soon as put in the ground. I have noticed ties taken up, after a short service of six to eight months, which were covered on the bottom by the branching mycelium, and after drying one eighth to one fourth of an inch in depth would crumble to dust. It takes much longer for the mycelium to destroy the heart-wood of the yellow-pine sleepers from the bottom and sides than when it has access to the ends. In the first case it must nearly destroy the small medullary cells to reach the various rings, while from the end it has a larger area of the rings, which it readily follows. Painting the ends of this timber offers but little protection if the slightest opening occurs, as a spore can enter, grow, and carry on its destruction for a long time before it shows exterior decay.
The mycelium of Lentinus lepideus (Fr.) is composed of small branching filaments, only measuring 0·0004 of an inch to 0·0008 of an inch in diameter. With it I generally find an abundance of crystals of one form of oxalate of lime, and many cells of other fungi in adherent masses. The destructive power of this fungus is very great, and is causing enormous losses to consumers of the yellow pine, which are not realized or even suspected. In the sap-wood of this timber the fungus Sphæria pilifera (Fr.) readily grows, piercing the resin ducts in the medullary rays, its hyphæ spreading to the upright resin canals, and, from its abundance and dark color, discolors this portion of the wood; which, if it remains damp and warm, the fermentation set up soon destroys the sap-wood. This fungus grows at a very low temperature, and is very destructive.
In new railroad-ties of yellow pine, which came from Georgia February, 1886, for the use of New York roads, the sap-wood was already discolored, and some new growths of Sphœria took place here in March. Initial decay has already commenced in those ties, which will be facilitated by the conditions occurring when they are placed in the road-bed.
Fig. 8 is that of Polyporous versicolor (Fr.), which is very common and abundant, and is attached by its margin to the wood so that its form is called dimidiate. Several caps usually project one over the Fig. 8.—Polyporous versicolor (Fr.). other,the lowest being the longest, each succeeding one above being shorter. On the under surface of each cap are the pores just visible to the eye, which bear the spores. The distinct colored bands or zones upon the upper surface give it a beautiful effect, as seen upon the wood it is destroying. It is easily found, as its substance is quite tough and dries before the insects and molds destroy it. It is generally abundant upon the sap-wood of white-oak piles, especially if the bark is left on after felling. It grows on the sap-wood of the white and red oak and chestnut ties; also upon the sap-wood of chestnut posts, and on the sap-wood and heart-wood of wild-cherry. As a rule, I found it more abundant on sap-wood of the oak than on chestnut ties. My observations refer to the entire length of the Boston and Albany Railroad, and many other roads in New England. The bark should be removed from piles and ties of the woods just mentioned, as it allows them to season and dry, checking the growth of this fungus; whether it is alone capable of destroying the heart-wood of chestnut ties has not been ascertained. I never found it growing there, but, instead, Fistulina hepatica—Agaricus Americanus (Pk.), Polyporus pergamemus (Fr.), Dædalea quercina (P.), and Polyporus hirsutus (Fr.), the latter being very abundant in old chestnut ties put in a temporary embankment at Worcester, Massachusetts. It was also abundant in the chestnut curbing of some of the unused hydrants.
The heart-wood of chestnut ties is not so quickly attacked by fungi as some other woods, most of them being removed on account of the mechanical destruction of the fibers under the rails before decay takes place. I have several specimens of mycelia in the heart-wood of chestnut ties, but have only found a few developed efforts of fructification.
Polyporous applanatus (Fr.) is frequently found upon the sap-wood of many oaks, and is the one I generally find upon the heart-wood of white-oak ties. It is usually dimidiate, as shown in Fig. 9, though, when growing upon the under side of timber above-ground, it is often resupinate; the pores all point downward, the substance of the cap is hard, and, if undisturbed, the pores in the next year's growth form Fig. 9.—Polyporous applanatus (Fr.). over that of the preceding years, but, enlarging the area, many of them are found twelve to eighteen inches across, and by cutting through them so as to show the section, six to eight years' growth is often seen. In this figure but one year's growth has taken place; frequently two caps form instead of only one, as here shown.
In white-oak timber and ties the earlier growth of the mycelium is not as continuous and uninterrupted as in the yellow pine, but grows more in little white patches, with considerable wood intervening between each. In Fig. 9 they are shown as dark spots. The massive bundles of medullary rays of this wood slowly decay, and preserve their form long after the other tissue has decayed. The large ducts seen in Fig. 3 are not open with a free communication, but filled with a delicate tissue, remains of which are visible in the cut; this tissue will be found quite perfect in ties well advanced in decay.
The fungi so far illustrated in this paper apply mostly to the decay of timber under conditions similar to those of railroad service. In the next paper I shall give two or three illustrations of fungi of more general character. To deal with the great practical question of preventing wood from decay, the subject requires a more special treatment than it has received. Each species of tree, to a great extent, has special fungi, as it has insects which are not common upon other kinds of wood. Red cedar, cypress, locust, and catalpa are very durable in contact with the ground, where some others would quickly decay. The chemical composition of woods is not practically the same, as recently stated, but differs even in the sap-and heart-wood of the same species. Some of the woods have compounds in their cells easily induced to decompose and start the wood-tissue, while others have different compounds requiring inducing agents of greater intensities to begin decay; and it is not true that a fungus which will destroy one wood will destroy all of the other species, and this one fact is of great practical importance, for, in a road-bed filled with the mycelium of one kind of decayed wood, another wood may be used which is not affected by that fungus, and its mycelium would be inert.
In treating wood it is found that the chemical which will prevent the germination of the spore of the fungus may not protect it from the attacks of its mycelium, contained in the ground or upon other decayed timber.
Experience has long since established the fact that wood kept perfectly dry will last for many hundreds of years, as has been the case in the roofs of foreign buildings, or when it is submerged in the water, as has been the case of piles used for foundations of the earlier bridges in older countries. Posts and telegraph-poles can daily be seen which are decaying near the ground-line, but sound above, after three to four years' service. By comparing the different conditions of use, it can be seen how little change is required to render unstable what would be stable under other circumstances. In roofs, the conditions are dryness, circulation of air, plenty of spores, and sufficient temperature to germinate, but the necessary moisture is absent. In the case of submerged piles, plenty of water, sufficient temperature, but exclusion of air, either to carry spores or permit them to grow. In the case of the posts and telegraph-poles we have the spores, the moisture, and the necessary temperature in summer for germination, and decay ensues from the fact that these are the essential conditions for the growth of the fungi whose work it is to undo and liberate the compounds in the woody tissue.