CHAPTER II.

ON THE GRADUAL RISE AND DEVELOPMENT OF DRY ROT.

The opinion generally received has drawn a line of discrimination between the decay accompanied by a vegetable spreading on the surface of the timber, and that which is effected by an animal existing within it, which decay is frequently denominated the worm in timber; but as each is equally entitled to the dreaded appellation, they might more justly be distinguished as the animal and vegetable rot.

The dry rot in timber derives its name from the effect produced, and not from the cause: it is so called in opposition to the wet rot, which is properly denominated, as this exists only in damp situations, and is applied to the decomposition which takes place in timber containing sap, and exposed to moisture: but although the dry rot is usually generated in moisture, in some cases it will flourish independent of extraneous humidity. Dry rot differs from wet rot in this respect, that the former takes place only when the wood is dead, whereas the latter may begin when the tree is standing.

Wet rots are composed of porous fibre running from the rot into the trunk of the tree. This rot is of a brown colour, and has an offensive smell. The evil is often found with white spots, the latter of watery substance: when it has yellow flames, it is very dangerous.

A large quantity of the vegetable kingdom consists of plants differing totally from the flowering plants in general structure, having no flowers and producing no seed properly so called, but propagating by means of minute cellular bodies, called _spores_. These highly organized vegetables are known to botanists as _Cryptogamia_. Fungi are plants in which the fructifying organs are so minute, that without the aid of a powerful microscope they cannot be detected. To the naked eye, the fine dust ejected from the plant is the only token of reproduction; this dust, however, is not truly seed, for the word seed supposes the existence of an embryo, and there is no such thing in the reproductive bodies of fungi. The correct terms are _spores_, when the seeds are not in a case; _sporidia_ when enclosed in cases. The spores or sporidia are placed in or upon the receptacle, which is of very various forms and kinds, but how different soever these may be, it is the essential part of the fungus, and in many cases constitutes the entire plant. That portion of the receptacle in which the reproductive bodies are imbedded is called the _hymenium_: it is either external, as in the Agaric, where it forms gills; or included, as in the puff-balls. The _pileus_ of fungi is the entire head of the plant, not a mere head covering.

Some naturalists have insisted upon the spontaneous production of fungi, while others maintain that they are produced by seed, which is taken up and supported in the air until a soil proper for its nourishment is presented, on which being deposited it springs up of various appearances according to the principle of the seed, and the nature of the recipient.

It is extremely difficult to give a logical definition of what constitutes a fungus. It is not always easy with a cursory observation under the microscope, to determine whether some appearances are produced by fungi, insects, or organic disease; experience is the safest guide, and until we acquire that we shall occasionally fail.

In the ‘Index Fungorum Britannicorum,’ 2479 species of British fungi are enumerated: any detailed account of the arrangement of this extensive family of plants, or of the character of even its principal sections would be impossible within the limits of this volume; all that can be attempted will be a general description of the fungi causing dry rot.

If dry rot shows itself in a damp closet or pantry, the inside of the china or delf lying there will be coated with a mould, or a fine powder like brick-dust. This excessively fine powder is no other than unaccountable myriads of the reproductive spores or _seeds_ of the fungus; they are red in colour, and are produced on the surface of the fungus in millions. Certain privileged cells on the face of the fungus are furnished each with four minute points at their apex, each four bearing a single brick-red, egg-shaped spore; so that the fruit is spread over the surface of the fungus in groups of fours. To see the form of these spores the highest powers of the microscope are required, and then they can only be viewed as transparent objects. If these excessively minute bodies be allowed to fall on wet flannel, damp blotting-paper, or wet wood, they immediately germinate and proceed to reproduce the parent fungus. The red skin of the spores cracks at both ends, and fine mycelial filaments are sent out: this is the “mould,” spawn, or mycelium from which the new fungus (under favourable conditions of continued moisture) appears.

It matters little where we go: everywhere we are surrounded with life. The air is crowded with birds and insects; the waters are peopled with innumerable forms, and even the rocks are blackened with countless mussels and barnacles. If we pluck a flower, in its bosom we see many a charming insect. If we pick up a fallen leaf, there is probably the trace of an insect larvæ hidden in its tissue. The drop of dew upon this leaf will probably contain its animals, visible under the microscope. The very mould which covers our cheese, our bread, our jam, or our ink, and disfigures our damp walls, is nothing but a collection of plants.

The starting point of life is a single cell-that is to say a microscopic sac filled with liquid and granules, and having within it a nucleus, or smaller sac. From this starting point of a single cell, this is the course taken: the cell divides itself into two, the two become four, the four eight, and so on, till a mass of cells is formed.

The researches of Pasteur show that atmospheric dust is filled with minute germs of various species of animals and plants, ready to develop as soon as they fall into a congenial locality. He concludes that all fermentation is caused by the germination of such infinitesimal spores. That they elude observation does not seem strange, when we consider that some infusoria are only ⅟240000 of an inch in length.

It is ascertained that fungi produce seed which contains the properties of germination; and that vegetable corruption is suited to effect it. When we contemplate the fineness and volatility of the germs, the hypothesis will not appear unreasonable that they are conveyed by the rains into the earth, and are absorbed by vegetables; that with the sap they are disseminated throughout the whole body, and begin to germinate as soon as the vegetable has proceeded to corruption. Whatever, therefore, may be the appearance or situation of the fungus producing the dry rot, or from whatever substance it originates, that substance must be in a corrupt state.

Fungi result from, or are attendant on, vegetable corruption, assisted by an adequate proportion of heat and moisture. The sap, or principle of vegetation, brought into activity, is, according to the ‘Quarterly Review,’ No. 15, the cause of dry rot, in as far as it is favourable to the growth of fungi, as it would seem to be when in a state of fermentation.

Vegetable corruption invariably presupposes fermentation.

Fermentation is a state of vegetable matter, the component parts of which have acquired sufficient force to produce an intestinal motion, by which the earthy saline, the oily and aqueous particles therein contained, exert their several peculiar attractive and repulsive powers, forming new combinations, which at first change, and at length altogether destroy the texture of the substance they formerly composed.

There are two things essential towards creating and supporting the intestinal motion, namely, heat and humidity; for without heat, the air, which is supposed to be the cohesive principle of all bodies, cannot be so rarefied as to resume its elasticity; and without humidity there can be no intestinal motion.

According to Baron Liebig, the decay of wood takes place in the three following modes:--First, oxygen in the atmosphere combines with the hydrogen in the fibre, and the oxygen unites with the portion of carbon of the fibre, and evaporates as carbonic acid: this process is called decomposition. Second, we have to notice the actual decay of wood which takes place when it is brought in contact with rotting substances; and the third process is called putrefaction. This is stated by Liebig to arise from the inner decomposition of the wood in itself: it loses its carbon, forms carbonic acid gas, and the fibre, under the influence of the latter, is changed into white dust.

The fungus occasioning the dry rot is of various appearances, which differ according to the situation in which it exists. In the earth, it is fibrous and perfectly white, ramifying in the form of roots; passing through substances from the external surface, it somewhat differs from that form; here it separates into innumerable small branches.

Mr. McWilliam observes, “If the fungi proceed from the slime in the fissures of the earth, they are generally very ramous, having round fibres shooting in every direction. If they arise from the roots of trees, their first appearance is something like hoar frost; but they soon assume the mushroom shape.”

Hence it appears that we frequently build on spots of ground which contain the fundamental principle of the disease, and thus we are sometimes foiled in our endeavours to destroy the fungus by the admission of air. In this case the disease may be encouraged by the application of air as a remedy. When workmen are employed in buildings which contain dry rot, and when they are working on ground which contains the symptoms of this disease, their health is often affected. A London builder informs us, that a few years since, while building some houses at Hampstead his men were never well: he afterwards ascertained that the ground was affected with rot, and that within one year after the house was erected, all the basement floor was in a state of premature decay. Sir Robert Smirke, architect, remarked in 1835, that he had noticed “there are certain situations in which dry rot prevails remarkably.”

The fungus protruded in a very damp situation is fibrous, of moderate thickness, feels fleshy. From the spot whence it arises it extends equally around, wholly covering the area of a circle. This form would possibly continue in whatever situation it might vegetate, if the air had no motion, and every part of the substance on which it grew were equally supplied with a matter proper to encourage the expansion. The surface of this fungus is pursed, and of various colours, the centre is of a dusky brown, mixed with green, graduated into a red, which degenerates into yellow, and terminates in white.

One of the most formidable of the tribe of fungi is the _Merulius lachrymans_ (often called _the_ Dry Rot) of which the following description is given by Dr. Greville: “Whole plant generally resupinate, soft, tender, at first very light, cottony, and white. When the veins appear, they are of a fine yellow, orange, or reddish brown, forming irregular folds, most frequently so arranged as to have the appearance of pores, but never anything like tubes, _and distilling, when perfect, drops of water_.” Hence the term _lachrymans_, from _lacrymo_, Lat., I weep: the _Merulius lachrymans_ is often dripping with moisture, as if weeping in regret for the havoc it has made. In the genus _Merulius_, the texture is soft and waxy, and the hymenium is disposed in porous or wavy toothed folds. Berkeley, in his ‘Fungology,’ gives the following description, which is similar to Dr. Greville’s: “Large, fleshy but spongy, moist, ferruginous yellow, arachnoid and velvety beneath; margin tomentose, white; folds ample, porous, and gyroso-dentate.” The _Merulius_ is found in cellars and hollow trees, sometimes several feet in width, and is the main cause of dry rot.

Another formidable fungi, which attacks oak in ships, is the _Polyporus hybridus_ (the dry rot of our oak-built vessels). It is thus described by Berkeley: “White, mycelium thick, forming a dense membrane, or creeping branched strings, hymenium breaking up into areæ, pores long, slender, minute.”

From the slow progress dry rot makes in damp situations, it appears that excessive damps are inimical to the fungus, for its growth is more rapid in proportion as the situation is less damp, until arrived at that certain degree of moisture which is suited both to its production and vegetation. When further extended to dry situations, its effects are considerably more destructive to the timber on which it subsists: here it is very fibrous, and in part covered with a light brown membrane, perfectly soft and smooth. It is often of much greater magnitude, projecting from the timber in a white spongeous excrescence, on the surfaces of which a profuse humidity is frequently observed: at other times, it consists only of a fibrous and thin-coated web irregularly on the surface of the wood. Excrescences of a fungiform appearance are often protruded amidst those already described, and are evidences of a very corrupt matter peculiar to the spots whence they spring. According to the situation and matter in which they are produced, they are dry and tough, or wet, soft, and fleshy, sometimes arising in several fungiforms, each above the other, without any distinction of stem; and when the matter is differently corrupted, it not unfrequently generates the small acrid mushroom.

Mr. McWilliam observes, “The fungi arising from oak timbers are generally in clusters of from three to ten or twelve; while those from fir timber are mostly in single plants: and these will continue to succeed each other until the wood is quite exhausted.”

Damp is not only a cause of decay, but is essential to it; while, on the other hand, absolute wet, especially at a low temperature, prevents it. In ships this has been particularly remarked, for that part of the hold of a ship which is constantly washed by the bilge-water is never affected with dry rot. Neither is that side of the planking of a ship’s bottom which is next the water found in a state of decay, even when the inside is quite rotten, unless the rot has penetrated quite through the inside.

It matters little whether wet is applied to timber before or after the erection of a building. Timber cannot resist the effect of what must arise in either case; viz. heat and moisture, producing putrid fermentation; for instance, in basement stories with damp under them, dry timber is but little better than wet, for if it is dry it will soon be wet; decay will only be delayed so long as the timbers are absorbing sufficient moisture, therefore every situation that admits moisture is the destruction of timber.

In a constancy and equality of temperature timber will endure for ages. Sir Christopher Wren, in his letter to the Bishop of Rochester, inserted in Wadman’s ‘History of Westminster Abbey,’ notices “That Venice and Amsterdam being both founded on wooden piles immersed in water, would fall if the constancy of the situation of those piles in the same element and temperature did not prevent the timber from rotting.” Nothing is more destructive to woodwork than _partial leaks_, for if it be kept _always wet_ or _always dry_, its duration is of long continuance. It is recorded that a pile was drawn up sound from a bridge on the Danube, that parted the Austrian and Turkish dominions, which had been under water 1500 years.

The writer of an article on the decay of wood, in the ‘Encyclopædia Britannica,’ 1855, observes, “If a post of wood be driven into the ground, the decay will commence at the surface of the ground; if driven into the earth through water, the decay will commence at the surface of the water; if used as a beam let into a damp wall, rot will commence just where the wood enters the wall.”

Humboldt observes in his ‘Cosmos,’ with reference to damp and damp rooms, that anyone can ascertain whether a room is damp or not, by placing a weighed quantity of fresh lime in an open vessel in the room, and leaving it there for twenty-four hours, carefully closing the windows and doors. At the end of the twenty-four hours the lime should be reweighed, and if the increase exceeds one per cent. of the original weight, it is not safe to live in the room.

Decay of timber will arise from the effects of continued dryness or continued wetness, under certain conditions; or it may also arise from the effect of alternate dryness and moisture, or continued moisture with heat.

At one time dry rot appears to have made great havoc amongst the wooden ships of the British Navy. In the Memoirs of Pepys, who was Secretary to the Admiralty during the reigns of Charles II. and James II., reference is made to a Commission which was appointed to inquire into the state of the navy, and from which it appears that thirty ships, called new ships, “for want of proper care and attention, had toadstools growing in their holds as big as one’s fists, and were in so complete a state of decay, that some of the planks had dropped from their sides.”

In the ‘European Magazine’ for December, 1811, it is stated that, “about 1798, there was, at Woolwich, a ship in so bad a state that the deck sunk with a man’s weight, and the orange and brown coloured fungi were hanging, in the shape of inverted cones, from deck to deck.”

Mr. William Chapman, in his ‘Preservation of Timber from Premature Decay,’ &c., gives several instances of the rapid decay of the ships of the Royal Navy, about the commencement of the present century. He mentions three ships of 74 guns each, decayed in five years; three of 74 guns each, decayed in seven years; and one of 100 guns, decayed in six years. Mr. Pering, also, in his ‘Brief Enquiry into the Causes of Premature Decay,’ &c., says that ships of war are useless in five or six years; and he estimates the average duration to be eight years, and that the cost of the hull alone of a three-decker was nearly 100,000_l._ Mr. Pering was formerly at the dockyard, Plymouth, and therefore a good authority, if he availed himself of the opportunities of studying the subject. He has stated that he has seen fungi growing so strong betwixt the timbers in a man-of-war, as to force a plank from the ship’s side half an inch.

No doubt a great deal of this decay was attributable to the use of unseasoned timber, and defective ventilation; but there is too much reason to believe that it was principally owing to the introduction of an inferior species of oak (_Quercus sessiliflora_) into the naval dockyards, where, we imagine, the distinction was not even suspected. The true old English oak (_Quercus robur_) affords a close-grained, firm, solid timber, rarely subject to rot; the other is more loose and sappy, very liable to rot, and not half so durable.

One cause of the decay of wood in ships is the use of wooden treenails. A treenail is a piece of cleft wood (made round), from 1 foot to 3 feet 6 inches in length and 1½ inch in diameter. As the treenails are also made to drive easy, they never fill the holes they are driven into; consequently, if ever it admits water at the outer end, which, from shrinking, it is liable to do, that water immediately gets into the middle of the plank, and thereby forms a natural vehicle for the conveyance of water. The treenail is also the second thing which decays in a ship, the first, generally, being the oakum. Should any part of the plank or timbers of a ship be in an incipient state of decay, and a treenail come in contact with it, the decay immediately increases, while every treenail shares the same fate, and the natural consequence is, the ship is soon left without a fastening. Treenails in a warm country are sure to shrink and admit water.

Mr. Fincham, formerly Principal Builder in Her Majesty’s dockyard, Chatham, considers that the destruction of timber by the decay commonly known as dry rot, cannot occur unless air, (?) moisture, and heat are all present, and that the entire exclusion of any of the three stays the mischief. By way of experiment, he bored a hole in one of the timbers of an old ship built of oak, whose wood was at the time perfectly sound; the admission of air, the third element, to the central part of the wood (the two others being to a certain degree present) caused the hole to be filled up in the course of twenty-four hours with mouldiness, which very speedily became so compact as to admit of being withdrawn like a stick.

The confinement of timber under most circumstances is attended with the worst consequences, yet a partial ventilation tends to fan the flame of decay.

The admission of air has long been considered the only means of destroying the fungus, but as it has frequently proved ineffectual, it must not be always taken as a certain remedy. If dry air be properly admitted, in a quantity adequate to absorb the moisture, it will necessarily exhaust and destroy the fungus; but care should be taken lest the air should be conveyed into other parts of the building, for, after disengaging itself from the fungus over which it has passed, it carries with it innumerable seeds of the disease, and destroys everything which offers a bar to its progress. Air, in passing through damps, will partake of their humidity; it therefore soon becomes inadequate to the task for which it is designed. Owing to this circumstance, air has been frequently admitted into the affected parts of a building without any ultimate success; too often, instead of injuring the fungus, it has considerably assisted its vegetation, and infected with the disease other parts of the building, which would otherwise probably have remained without injury. The timber, which is in a state of decomposition by an intestinal decay, is little affected by the application of air, as this cannot penetrate the surrounding spongeous rottenness which generally forms the exterior of such timber, and protects the action which the humid particles have acquired in the exterior: as the extent and progress of the disease is therefore necessarily concealed, it is difficult to ascertain correctly the effect produced by the admission of dry air. Under these circumstances of necessity and danger, it will require considerable skill to effect the purpose without increasing the disease, and, as each case has its own peculiar characteristics, it is necessary before one attempts to admit air as a remedy, to previously estimate the destructive consequences which may result from so doing, and ascertain whether it will be injurious or beneficial to the building. The joists of the houses built by our ancestors last almost for ever, because they are in contact with an air which is continually changing. Now, on the contrary, we foolishly enclose them between a ceiling of plaster (always very damp to begin with) and a floor; they frequently decay, and then cause the most serious disasters, of which it is impossible to be forewarned.

Damp, combined with warmth, is as a destroying agent, still more active than simple damp alone--the heat being understood as insufficient to carry off the moisture by evaporation; and the higher the temperature with a corresponding degree of moisture, the more rapid the decay. If the temperature to which wood is exposed, whilst any sap remains in it, is too elevated, the vegetable fluids ferment; the tenacity is diminished, and when the action is carried to its full extent, the wood quickly becomes affected by the dry rot. Exposure to the atmosphere in positions where rain can lodge in quantity, contact with the ground, and application in damp situations deprived of air, will render wood liable to the wet rot; and however well seasoned it may have been previously to being brought within the influence of any of these causes, it will infallibly suffer. Air should therefore have free access to the wood in every direction:

… “for without in the wall of the house he made narrowed rests round about, that the beams should not be fastened in the walls of the house.”--1 Kings vi. 6.

Rondelet says, “The woodwork of the church of St. Paul, outside the city walls, which was destroyed by fire in 1823, was erected as far back as the fifth century.” Although the atmosphere surrounding the framework was often at once warm and damp, yet it was never stagnant. It should be remembered that 500 people in a church during two hours give off fifteen gallons of water into the air, which, if not carried away, saturates everything in the building after it has been breathed over and over again in conjunction with the impurities it contains collected from each individual.

Fever, scrofula, and consumption arise in many instances from defective ventilation.

The signs of decay in timber are, as has been stated, fungi. Some of them now and then are microscopic, and owe their existence to the sporules deposited on the surface; while fermentation, generated by prolonged contact with warm, damp, and stagnant air, is as a soil where seeds sow and nourish themselves.

Mr. McWilliam, in his work on dry rot, states that if the temperature be very low or very high, the effects are the same with respect to the growth of fungi. At 80° dry rot will proceed rapidly, at 90° its progress is more slow; at 100° it is slower still, and from 110° to 120° it will in general be arrested. It will proceed fast at 50°; it may be generated at 40°; its progress will be slow at 36°; and is arrested at 32°, yet it will return if the temperature is raised to 50°.

Dry rot externally first makes its appearance as a mildew, or rather a delicate white vegetation, that looks like such. The next step is a collecting together of the fibres of the vegetation into a more decided form, somewhat like hoar frost; after which it speedily assumes the leathery, compact character of the fungus, forming into leaves, spreading rapidly in all directions, and over all materials, and frequently ascending the walls to a considerable height, the colour variable--white, greyish white, and violet, light or decided brown, &c.

In the section of a piece of wood attacked by dry rot a microscope reveals minute white threads spreading and ramifying throughout its substance; these interlace and become matted together into a white cottony texture, resembling lint, which effuses itself over the surface of the timber; then in the centre of each considerable mass a gelatinous substance forms, which becomes gradually of a yellow, tawny hue, and a wrinkled, sinuated porous consistence, shedding a red powder (the spores) upon a white down; this is the resupinate pileus, the hymenium being upwards, of _Merulius lachrymans_, in its perfect and matured state. Long before it attains to this, the whole interior of the wood on which it is situated has perished; the sap vessels being gradually filled by the cottony filaments of the fungus; no sooner do these appear externally than examination proves that the apparently solid beam may be crumbled to dust between the fingers; tenacity and weight are annihilated.

Dr. Haller says that seven parts in eight of a fungus in full vegetation are found by analysis to be completely aqueous.

The strength of fungi is proportionate to the strength of the timber the cohesive powers and nutritive juices of which they absorb; and according to the food they receive so they are varied and modified in different ways, and are not always alike. Different stages of corruption produce food of different qualities, and hence many of the different appearances of fungi. One takes the process of corruption up where another leaves it off, and carries it forward and farther forward to positive putrefaction.

The forms which fungi assume are extremely diversified; in some instances we have a distinct stem supporting a cap, and looking somewhat like a parasol; in others the stem is entirely absent, and the cap is attached either by its margin, and is said to be _dimidiate_, or by its back, or that which is more commonly its upper surface, when it is called _resupinate_. In some species the form is that of a cup, in others of a goblet, a saucer, an ear, a bird’s nest, a horn, a bunch of coral, a ball, a button, a rosette, a lump of jelly, or a piece of velvet.

Decomposition takes place without fungus where the timber and the situation are always moist, as in a close-boarded kitchen floor, where it is always dry, or very nearly so, and where it is alternately wet and dry, cold and hot. When the decomposition is affected with very little moisture, and no fungus, the admission of air will generally prevent further contamination; but where there is abundance of moisture, rottenness, and fungus, a small quantity of air will hasten the destruction of the building.

In timber which has been only superficially seasoned this disease is produced internally, and has been known to convert the entire substance of a beam, excepting only the external inch or two of thickness to which the seasoning had penetrated, into a fine, white, and threadlike vegetation, uniting in a thick fungous coat at the ends, the semblance being that of a perfectly sound beam. In this internal rot a spongy fungous substance is formed between the fibres. This has often been observed in large girders of yellow fir, which have appeared sound on the outside, but by removing some of the binding joists have been found completely rotten at the heart. An instance of this kind occurred at Kenwood (the seat of the Earl of Mansfield) in 1815. Major Jones, R.E., states that on one occasion he was called upon to report on the state of a building in Malta; that the timbers had every external appearance of being sound, but on being bored with an auger they were found internally in a total state of decay. It is on this account that the practice of sawing and bolting beams is recommended, for when timber is large enough to be laid open in the centre this part is laid open to season; so that when a tree is large enough to be cut through to make two or more beams, decomposition is impeded.

The first symptoms of rottenness in timber are swelling, discoloration, and mouldiness, accompanied with a musty smell; in its greater advance the fibres are found to shrink lengthways and break, presenting many deep fissures across the wood; the fibres crumble readily to a fine snuff-like powder, but retain, when undisturbed, much of their natural appearance.

In whatever way boughs are removed from trees, the effect of their removal is, however, very frequently to produce a rotting of the inner wood, which indicates itself externally by a sudden abnormal swelling of the trunk a little above the root; sometimes the trunk becomes hollow at the part affected, and this particular description of rot will almost invariably be found to exist in those trees whose roots are much exposed. The rot itself is either of a red, black, or white colour in the timber when felled, and when either of the two last-named colours prevail, it will be found that the decay does not extend very far into the tree; but if, on the contrary, the colour of the parts most visibly affected should be decidedly red, the wood should be rejected for any building purposes. Sometimes small brown spots, indicative of a commencement of decay, may be observed near the butt or root end of trees, and though they do not appear to be connected with any serious immediate danger to the durability of the wood, it is advisable to employ the material so affected only in positions where it would not be confined in anything like a close, damp atmosphere.

Great hesitation may be admitted as to the use of timber which presents large bands of what are supposed to be indefinitely-marked annual growth, because the existence of zones of wood so affected may be considered to indicate that the tree was not in a healthy state when they were formed, and that the wood then secreted lacked some of the elements required for its durability, upon being subsequently exposed to the ordinary causes of decay.

In many cases when timber trees are cut down and converted for use, it is found that at the junction of some of the minor branches with the main stem, the roots, as it were, of the branches traverse the surface wood in the form of knots, and that they often assume a commencement of decay, which in the course of time will extend to the wood around them. This decay seems to have arisen in the majority of cases from the sudden disruption of the branch close to its roots, with an irregular fracture, and with such depressions below the surface as to allow the sap to accumulate, or atmospheric moisture to lodge in them. A decomposition of the sap takes place--in fact, a wound is made in the tree-and what are called “druxy knots” are thus formed, which have a contagious action on the healthy wood near them.

There is this particular danger about the dry rot; viz. that the germs of the fungi producing it are carried easily, and in all directions, in a building wherein it once displays itself, without necessity for actual contact between the affected or the sound wood; whereas the communication of the disease resulting from the putrefactive fermentation, or the wet rot, only takes place by actual contact.

Before dry rot has time to destroy the principal timbers in a building, it penetrates behind the skirtings, dadoes, and wainscotings, drawing in the edges of the boards, and splitting them both horizontally and vertically. When the fungus is taken off, they exhibit an appearance similar both in back and front to wood which has been charred; a light pressure with the hand will break them asunder, even though affected with the rot but a short time; and in taking down the wainscot, the fibrous and thin-coated fungus will generally be seen closely attached to the decayed wood. In timber of moderate length the fungus becomes larger and more destructive, in consequence of the matter congenial to its growth affording a more plentiful supply.

It is a great characteristic of fungi in general that they are very rapid in growth, and rapid in decay. In a night a puff-ball will grow prodigiously, and in the same short period a mass of paste may be covered with mould. In a few hours a gelatinous mass of _Reticularia_ will pass into a bladder of dust, or a _Coprinus_ will be dripping into decay. Many instances have been recorded of the rapidity of growth in fungi; it may also be accepted as an axiom that they are in many instances equally as rapid in decay.

In considering the liability of any particular description of foreign timber to take the dry rot, attention must be paid to the circumstances under which it is imported. Sometimes the timber is a long while coming here, whilst at other times it is imported in a very short period. The length of time consumed in the voyage has a great deal to do with its likelihood of taking the rot: it may have a very favourable passage, or a very wet one, and the ship is frequently, in some degree, affected with the disease. It perhaps begins in the ship, and it may often be seen between the timber or deals, when it will impregnate the wood to a great depth. Whether it is inherent in the timber or not, of this we may be certain, that where there is a fetid atmosphere it is sure to grow. Canadian yellow wood pine timber is more subject to rot than Baltic or Canadian red wood timber, although the latter will sometimes decay in four or five years. Turpentine is a preventive against dry rot, and Canadian timber is sometimes largely impregnated with it, especially the red wood timber; the yellow wood is very subject to dry rot. Very few cargoes of timber in the log arrive from Canada in which in one part or other of nearly every log you will not see a beginning of the vegetation of the rot. Sometimes it will show itself only by a few reddish, discoloured spots, which, when scratched by the finger nail to the extent of each spot, it will be seen that the texture of the timber to some little depth is destroyed, and will be reduced to powder; and on these spots a white fibre may generally be seen growing. If the timber has been shipped in a dry condition, and the voyage has been a short one, there may be a few logs without a spot; but generally speaking very few cargoes arrive from Canada in which there are many logs of timber not affected. But if the cargo has been shipped in a wet condition, and the voyage has been a long one, then a white fibre will be seen growing over nearly every part of the surface of every log; and in cargoes that have been so shipped, all the logs of yellow pine, red pine, and of oak, are generally more or less affected on the surface.

Nearly every deal of yellow pine that has been shipped in Canada in a wet state, when it arrives here is also covered over with a network of little white fibres, which are the dry rot in its incipient state. There is no cargo, even that which is shipped in tolerably dry condition, in which, upon its arriving here, may not be found some deals, with the fungus beginning to vegetate on their surface. If they are deals that have been floated down the rivers of America or Canada, and shipped in a wet state, on their arrival here they are so covered with this network of the fungus, that force is often necessary to separate one deal from another, so strongly does the fungus occasion them to adhere. They grow together again, as it were, after quitting the ship, while lying in the barges, before being landed. Accordingly, if a cargo has arrived in a wet condition, or late in the year, or if the rain falls on the deals before they are landed, and they are then piled in the way in which Norwegian and Swedish deals are piled, that is, flatways, in six months time, or even less, the whole pile of deals become deeply affected with rot; so that, whenever a flat surface of one deal is upon the flat surface of another, the rot penetrates to the depth of ⅛ of an inch. Its progress is then arrested by repiling the deals during very dry weather, and by sweeping the surface of each deal before it is repiled: but the best way is to pile the deals in the first instance upon their edges; by which means the air circulates freely around them, the growth of the fungus is arrested, and the necessity of repiling them prevented. If the ship is built of good, sound, and well-seasoned oak, the rot would perhaps not affect it, but in order to prevent its doing so, the precaution is usually taken to scrape the surface as soon as the hold is clear of the cargo of timber. Were the cargo not cleared, and the hold not ventilated, a ship that was permanently exposed to this fungus would, no doubt, be affected. It is easy, however, to prevent its extending by washing the hold with any desiccating solution.

Anyone who wishes to know how timber is occasionally shipped to this country should read the report of a trial, in the ‘Times,’ 22nd Feb., 1875 (Harrison _v._ Willis), relative to a cargo of pitch pine shipped from Sapelo, in the Isthmus of Darien, for Liverpool. This cargo, however, never arrived at Liverpool: it was lost at sea.

The motto of the Worshipful Company of Shipwrights is, “Within the ark, safe for ever.” We suggest it should be altered to, “Within the ark _which is free from dry rot_, safe for ever.”

There are two descriptions of European deals very liable to take the dry rot; viz. yellow Petersburgh deals, and yellow and white battens, from Dram, in Norway. When Dram battens, which have been lying a long time in bond in this country, have not been repiled in time, they have been found as much affected with the dry rot as many Canadian deals; though this has not happened in so short a time as has been sufficient to rot Canadian deals. The fungus growing on the Petersburgh deals and Dram battens has all the characteristics and effects of dry rot as exhibited in the Canadian deals, the detection of dry rot being in most cases the same.

It should be remembered that white deal absorbs more water than yellow; and yellow more water than red; and the quantity of water absorbed by the white accounts for its more rapid decay in external situations; as the greater the quantity of water absorbed the quicker is the timber destroyed. Mr. John Lingard, in his work on timber (1842), states that he has proved that 4½ oz. of water can be driven off from a small piece of fir, weighing only 10 oz. when wet, which is nearly half. This timber was on a saw-pit, and going to be put into a building.

The most general, and the most fatal cause of decay, viz. the wet rot, has attracted less attention than the more startling, but less common evils, the dry rot, and the destruction by insects.

Sir Thomas Deane, in 1849, related before the Institution of Civil Engineers of Ireland, an extraordinary instance of the rapid decay of timber from rot, which occurred in the church of the Holy Trinity at Cork.

On opening the floors under the pews, a most extraordinary appearance presented itself. There were flat fungi of immense size and thickness, some so large as almost to occupy a space equal to the size of a pew, and from 1 to 3 inches thick. In other places fungi appeared, growing with the ordinary dry rot, some of an unusual shape, in form like a convolvulus, with stems of from a quarter to half an inch in diameter. When first exposed, the whole was of a beautiful buff colour, and emitted the usual smell of the dry-rot fungus.

During a great part of the time occupied in the repairs of the church, the weather was very rainy. The arches of the vaults having been turned before the roof was slated, the rain water saturated the partly decayed oak beams. The flooring and joists, composed of fresh timber, were laid on the vaulting before it was dry, coming in contact at the same time with the old oak timber, which was abundantly supplied with the seeds of decay, stimulated by moisture, the bad atmosphere of an ill-contrived burial-place, and afterwards by heat from the stoves constantly in use. All these circumstances account satisfactorily for the extraordinary and rapid growth of the fungi.

Many instances might be mentioned of English oak being affected with dry rot, under particular circumstances. There was a great deal at the Duke of Devonshire’s, at Chiswick, about 60 years ago. Needy builders, who work for contract, sometimes use American oak, and call it wainscot: it is a bad substitute for wainscot, being very liable to warp and to be affected with dry rot. “I know of one public building,” observed the late Mr. Henry Warburton, M.P., “in which it has been introduced, and, I suppose, paid for under that name.”

Another serious instance of the decay of timber from rot occurred some time since in Old St. Pancras Church, London. When the dry rot made its appearance, it spread with amazing rapidity. Sometimes in the course of a night, a fungus of about the consistence of newly-fallen snow, and of a yellowish-white unwholesome colour, would be found to have spread over a considerable surface. The fungus was without shape, but in some cases it rose to a height of 2, 3, or 4 inches above the planks or other surfaces on which it grew. It could be cut with a knife, leaving a clear edge on each side, and there did not seem to be any covering or membrane over the outer or under surface. The smell of those matters was unpleasant, and seemed like the concentration of the smell which had pervaded the church for so long a time before; and, in a short time, beams, planks of flooring, railings, &c., were reduced to rottenness: the colour changed, and a heavy dark-brown dust fell, and represented the once solid timber. On making an examination with a view of discovering the cause of the attack, it was found that in the graveyard, near the church, there were graves, and several vaults: there were also vaults in the inside of the church. Most of them were filled, or nearly so, with water, which had run from the overcrowded graves.

In the interior there were water-logged vaults, and the walls were saturated with damp. It was also seen that from want of proper spouts and drains, near the outer walls, the drip from the large pent roof had fallen into the foundations. In this situation, when the window frames were properly arranged, a drain dug round and from parts of the church, and other alterations, which should long before have been made, were completed, the dry rot vanished, and no more complaints of the foulness of the air have since been heard.

We could quote many cases of rot which have been caused from the want of proper drains and spouts. Architects should remember that the feet of Gothic collar roofs have to bear the whole weight of the roof, and unless well seasoned, and carefully protected from damp, leaks, &c., premature decay and dry rot will be sure to occur. It is surprising what injury leaks from gutters will sometimes do. In 1851, Professor T. L. Donaldson stated that “a brestsummer of American timber was used some time since at a house in London: after an expiration of three years cracks began to appear in the front wall. A friend of mine, an architect, was called in to find out the cause; and after examining different parts of the house, was almost giving up his search in despair, when he thought he would have the shop cornice removed and look at the brestsummer. He then discovered that some water had been admitted by accident, and penetrating the brestsummer, had caused it to rot, and crack the wall.”

Dry rot was found in the great dome of the Bank of England, London, as originally built by Sir Robert Taylor: it also existed in the Society of Arts building, in the Adelphi, London. It was also found in the domes of the Panthéon, and Halle-au-Blé, Paris; but we hope there is no dry rot in the dome of St. Paul’s Cathedral, London, which is constructed entirely of timber, covered externally with lead.

The decayed state of a barn floor attacked by rot is thus described by Mr. B. Johnson: “An oak barn floor which had been laid twelve years began to shake upon the joists, and on examination was found to be quite rotten in various parts. The planks, 2½ inches in thickness, were nearly eaten through, except the outsides, which were glossy, and apparently without blemish. The rotten wood was partly in the state of an impalpable powder, of a snuff colour; other parts were black, and the rest clearly fungus. No earth was near the wood.” This oak was probably of the _Quercus sessiliflora_ species; and there was no ventilation to the floor.

Mr. John Armstrong, carpenter, employed for many years at Windsor Castle, observed: “I was employed a few years back at a house where I found a floor rotten. We took it up; it was yellow pine; it was laid in the damp, but on sleepers, and the sleepers were not rotten: they were of a different description of wood.” Probably the sleepers were of Baltic red wood.

Dr. Carpenter relates an instance of the expansive power resulting from the rapid growth of the soft cellular tissue of fungi. About the commencement of this century the town of Basingstoke was paved; and not many months afterwards the pavement was observed to exhibit an unevenness which could not easily be accounted for. In a short time after, the mystery was explained, for some of the heaviest stones were completely lifted out of their beds by the growth of large toadstools beneath them. One of these stones measured 22 inches by 21 inches, and weighed 83 lb., and the resistance afforded by the mortar which held it in its place would probably be even a greater obstacle than the weight. A similar incident came under the notice of Mr. M. C. Cooke (the author of ‘British Fungi’), of a large kitchen hearthstone which was forced up from its bed by an under-growing fungus, and had to be relaid two or three times, until at last it reposed in peace, the old bed having been removed to the depth of 6 inches, and a new foundation laid. A circumstance recorded by Sir Joseph Banks is still more extraordinary, of a cask of wine which, having been confined for three years in a cellar, was, at the termination of that period, found to have leaked from the cask, and vegetated in the form of immense fungi, which had filled the cellar, and borne upwards the empty wine cask.

Timber decay in contact with stone is a subject deserving consideration. This decay is entirely obviated by inserting the wood in an iron shoe, or by placing a thin piece of iron between the wood and the stone. It is said that a hard crust is formed on the timber in contact with the iron, which seems effectually to preserve it; it is, of course, necessary that a free circulation of air round the ends of the timber be provided. The most notable instance of timber decay in contact with stone with which we are acquainted occurred at the coronation of George IV. Westminster Hall was then fitted up, and they began by laying sleepers of yellow pine. The coronation was suspended for twelve months, and when the sleepers were taken up from the floor of Westminster Hall, they were in a rotten state.

Timber in contact with brickwork is in Suffolk and in some parts of England covered with sheet lead to preserve it from the effects of the damp mortar. Fungi will arise in mortar, if made with road-drift, and water from stagnant ponds, &c., and it may be traced through the mortar joints, and will thus appear on both sides of a wall. Mortar composed of unwashed sand will generate fungi; sea sand, even if washed, should never be used. It is considered that the system of grouting contributes to the early decay of timber; wood bond timber for walls has been consequently replaced by hoop iron bond. In Manchester wood bond is frequently used, and is said to answer well, but the high temperature of the buildings may be a preventive against the decay of timber, as the walls are soon dried. The practice is a bad one.

When timber used as posts inserted in the ground is placed in the inverted position to that in which it stood when growing, it is said to be very much more durable than if placed in its natural or growing position. This is easily accounted for in the valves of the sap vessels of the growing timber opening upwards; but when that position is inverted, the valves of the sap vessels become reversed in their action; and, therefore, when timber is used as posts inserted in the ground, the valves being so reversed prevent the ascent of moisture from the soil in the wood. Mr. W. Howe relates an experiment made to test the comparative durability of posts set as they grew. He says, “Sixteen years ago I set six pairs of bar posts all split out of the butt end of the same white oak log. One pair I set butts down; another pair, one butt down, the other top down; the others top down. Four years ago those set butt down were all rotted off, and had to be replaced by new ones. This summer I had occasion to reset those that were set top down: I found them all sound enough to reset. My experiments have convinced me that the best way is to set them tops down.” Other instances might be given in favour of placing posts in an inverted position in the ground. Posts will sometimes decay, for the following reason: The ends are often sawn off with a coarse implement and left spongy, with the longitudinal fibres shaken or broken a considerable way within the extremity of the wood. In this state the ends of the posts must be apt to absorb from the ground the moisture, which, being retained, and speedily pervading the whole internal surface, _especially if painted_, appears to cause decay.

With respect to the preservation of wooden fences, Mr. Cruikshank, of Marcassie, gives in detail various experiments from which it appears that--1st. When larch or pine wood is to be exposed to the weather, or to be put in the ground, no bark should be left on. 2nd. When posts are to be put in the ground, no earth should be put round them, but stones. 3rd. When a wooden fence is to be put up, a No. 4 or No. 5 wire should be stretched in place of, or alongside the upper rail.

Mr. G. S. Hartig, in the ‘Revue Horticole,’ gives the results of experiments made with great care and patience, upon woods buried in the earth. Pieces of wood of various kinds 3⅛th inches square, were buried about one inch below the surface of the ground, and they decayed in the following order: the lime, American birch, alder, and the trembling-leaved poplar, in three years; the common willow, horse-chestnut, and plane, in four years; the maple, red beech, and common birch, in five years; the elm, ash, hornbeam, and Lombardy poplar, in six years; the oak, Scotch fir, Weymouth pine, and silver fir, were only decayed to the depth of half an inch in seven years; the larch, common juniper, red cedar, and arbor vitæ, at the end of the last-mentioned period remained uninjured. The duration of their respective woods greatly depends on their age and quality; specimens from young trees decaying much quicker than those from sound old trees; and, when well seasoned, they, of course, last much longer than when buried in an unseasoned state. In experiments with the woods cut into thin boards, decay proceeded in the following order: the plane, horse-chestnut, poplar, American birch, red beech, hornbeam, alder, ash, maple, silver fir, Scotch fir, elm, Weymouth pine, larch, locust oak.

Before quitting the subject of decay of timber when buried in the earth, it will not be out of place to allude to the decay of railway sleepers, taking for example those in India: English and American sleepers will be dealt with more in detail hereafter.

Dr. Cleghorn, Conservator of Forests, Madras Presidency, India, considers the decay of sleepers to arise in a great measure from the inferior description of wood used. Mr. Bryce McMaster, Resident Engineer, Salem, considers that the native wood sleepers in India have hitherto been found for the most part to fail on the Madras Railway, between 30 and 40 per cent. requiring to be renewed annually. Mr. McMaster undertook an investigation with a view of ascertaining the causes of this deterioration, and whether those causes could be overcome so as to render available the vast resources of India. Thirteen hundred sleepers of sixteen different woods were submitted to careful examination and scrutiny twice at an interval of one year. The sleepers were variously placed, both on embankments and in cuttings; in some cases they were entirely covered with ballast to a depth of 4 inches; while in others they were as much as possible uncovered, and completely so from the rails to the ends--the ballast being only raised 2 inches in the middle of the way, and sloped off so as to carry away the water under the rails. From these observations it appeared that only five woods, Chella wungé, Kara mardá, Palai, Karúvalem, and Ilupé, were sound at the end of two years, the other eleven not lasting even that time. Also, that when the sleepers were uncovered, decay was less rapid than when they were buried in the ballast. The plan of leaving the sleepers partially uncovered had many advantages; it effected a saving of the ballast, allowed the defects to be more quickly detected, and kept the sleepers drier. It had been urged that the heat of the sun would split the sleepers and cause the keys and treenails to shrink; but from experience it was found that while among the “uncovered” sleepers there was a large proportion “beginning to split,” or “useless from being split,” there was on the other hand, among the “covered” sleepers, a still larger proportion “beginning to rot,” or “useless from being rotten.” It was also noticed that of the sleepers “beginning to rot,” 19 per cent. had commenced under one or both chairs. This was due to the retention of moisture under them, and might be remedied by tarring the seats of the chairs. As regarded the treenails where the sleepers were rotten, the treenails were invariably found to be in the same state; while, when the heads were exposed to the sun, they were not loosened by shrinking. Another objection was, that the road would be more likely to buckle and twist, but this was not found in practice to be the case. Treenails made in India cost 2_l._ 10_s._ to 4_l._ per 1000, and the woods generally used for the purpose are Vengé, Kara mardá, Erul, Porasa, or satin wood, and Trincomalee. The three woods first named are also extensively employed for keys, but teak keys seem to be the best, and their cost does not exceed 6_l._ per 1000. From the experience of the Indian engineers it appears that Teak, Saul, Sisso, Pedowk, Kara mardá, Acha, Vengé, Chella wungé, Palai, Erul, Karúvalem, will make very good sleepers to be used plain.

The sleepers which have failed on the Madras Railway might well be divided into two classes,--those which were originally of perishable woods, and were therefore unfit for the purpose; and those which although of good wood had been cut from young trees, and not been allowed to stand until old enough. The first arose from want of experience of the nature of Indian woods: the second from the absence of a proper system of working the jungles.

The wooden sleepers on the Indian railways should be tarred under the seats of the chairs, be laid in dry ballast, and raised slightly in the middle, and sloped off so as to throw the water under the rails. About two-thirds of the Indian woods are practically useless owing to the want of proper artificial means for preserving those of a perishable nature.

The subject of the decay of wood in India and tropical climates is too extensive to be further considered here; but is of sufficient importance to demand a volume to itself; the renewal of decayed wooden sleepers to railways forming annually a most important item in foreign railway budgets.

We have heard that some of our fortifications which have been erected within the last few years to protect our English coast from invasion, have already been invaded by dry rot. If this be true, some one well acquainted with the subject should at once be appointed to find out the cause, and recommend the remedy in each case.

Professional men, if they wish their works to “live for ever,” should consider the after consequences of neglecting to provide against dry rot. If the fungi could speak from under floors, ceiled-up roofs, behind wainscots, girders, &c., we should often hear them exclaim, “A nice moist piece of wood! Surely this belongs to us.” On the beams of a building at Crawley, a carpenter many years ago cut a few words; they are full of meaning in connection with our subject, and they run as follows:

“Man of weal, beware; beware before of what cometh behind.”