This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
23. The soil in which timber is grown exercises an important influence upon its quality; where damp and marshy, the fiber is of a light, spongy character, the excess of water preventing the healthy action of the sap in forming firm and compact wood. Such soil is better adapted to the growth of light woods, as basswood, willow, and white-wood.
The hard woods thrive best on dry, clayey soils, while those of the pine group are best developed in sandy soils.
24. Exposure to prevalent wind storms in one direction tends to produce a twisted, spiral mode of growth. Timber possessing this character is of little value for building purposes, because, when cut into planks or scantlings, the fibers run obliquely across them, and, therefore, it possesses little strength.
25. Trees are subject to excrescences and tumors which deteriorate the value of the timber. These may result from the defective nature of the soil, the attacks of animals by gnawing, or by insects which bore into the fiber.
An excess of sap in some parts of the tree shows on the outer surface by the formation of pus, or matter, which expends the virtue of the sap and deteriorates the value of the surrounding fiber. This disease may spread, and ultimately cause the death of the tree. Trees are also affected by a brownish rust, which is caused by rain water obtaining access to the cambium layers by means of clefts or rifts in the bark, and which, changing the character of the sap, reduces the wood to a powder.
These clefts in the bark may be the result of an unusually dry season and a rapid rising of the temperature, causing strains greater than the bark can resist; or they may be caused by severe frosts, which, acting on the sap, cause it to expand and rend the bark.
Frequently the clefts penetrate the sap wood also, and extend into the perfect woody layers. Though these separations of the fibers may be healed up by subsequent growth, they still cause a deterioration of the wood adjacent to them.
26. There is a species of insects which deposit their eggs in the clefts of the bark, where they are hatched. These insects are a kind of beetle, and, like the moth and butterfly, pass through a larval and pupal stage of development.
The larva, or grub, which is hatched from this egg, immediately bores into the sap wood, which furnishes its food.
The juices of the sap wood are composed of various substances - acids, albuminoids, gums, sugar, starch, oils, and water - on which the grub feeds and thrives, until it reaches its full size, when it weaves a chrysalis, or envelope-like sheath, and enters the pupa stage. This is a state of rest, in which the grub exists without nutriment while its organization is being elaborated, when it rends the envelope and emerges a perfect insect.
As the larval period extends for months, and sometimes years, during which the grub steadily eats its way into the fiber, it will be seen how destructive the operations of an innumerable army of these workers are, when once they obtain an opportunity to attack the timber.
Were it not for the warfare waged on these herbivorous insects by birds, squirrels, lizards, etc., which eagerly devour them, and for the action of frosts and rains, tending to prevent their excessive development, few trees would reach a state of maturity and be able to furnish sound, solid timber.
Where timber has been attacked by insects, the part affected, as well as the adjacent fiber, is rendered entirely useless for building purposes.
Where the stem of a tree is regularly formed, and shows a perfect bark, free from rifts and excrescences, it may be assumed that it will produce perfect timber.
27. In order to keep the timber perfect, however, the greatest care must be exercised in piling the timber, so as to prevent the attack of parasitic plants, called fungi. These constitute a lower order of plant life, which, instead of independently assimilating and digesting nourishment extracted from the soil, derive their nutriment from the organic substance of others.
The fungi are developed from spores, or life germs, which insinuate themselves into cracks and crevices, and propagate very rapidly. The vegetative system of these plants consists of filiform, or thread-like tubes, which form the roots and extract their food from the substance of the timber.
The interwoven tangle of these root hairs forms what is called the mycelium, which may retain the thread-like appearance of the roots, when it is defined as filamented; it may-become so closely woven as to appear like a sheet of paper, when it is called membranous; or when it presents an appearance like moss, with stems and branches, in which the fibers have become firm and hard, it is called fibrous.
As the mycelium grows and reaches maturity it sends out thread-like shoots of closer texture than the roots, and these shoots produce the spore cases which envelope the germinal seed.
The conditions which are considered favorable to the reception and germination of the spores of the fungi, are warmth, moisture, the exemption of sunlight, and the presence of elements suited for their nutrition.
The substance of the timber is attacked by the mycelium either by robbing it of the valuable juices contained in its fiber ducts, reducing the texture to a dry, lifeless, spongelike condition, or by secreting peculiar juices which act on the woody tissue and convert it again into cellulose (the starchy substance of its original formation), and which is dissolved and absorbed by the parasite, thus breaking down or decomposing the fiber, and resulting in what is known as decay or rot.
The conditions being favorable, the work of this insidious foe continues until the entire fabric is reduced to powder. The parasite attacks the living tree as well as cut timber, and in both cases the results are the same.