| Dry Rot on Floor Joist | [Frontispiece] |
| To face page | |
| Timber Beams—Rotten at the Heart | [34] |
| Baltic Modes of Cutting Deals | [64] |
| Mr. Kyan’s Timber Preserving Tank | [126] |
| Messrs. Bethell and Co.’s Timber Preserving Apparatus | [136] |
| Timber Piles from Balaclava Harbour | [208] |
| Destruction of Timber Pile by Teredo | [212] |
| Shell and Cell of Teredo navalis | [216] |
| Piles, Southend Pier; Limnoria, &c. | [220] |
| Carpenter Bees at Work | [260] |
A TREATISE ON DRY ROT IN TIMBER.
CHAPTER I.
ON THE NATURE AND PROPERTIES OF TIMBER.
In considering the subject of Timber trees, we commence with their Elementary Tissues, and first in order is the Formative Fluid, which is the sole cause of production of every tissue found in trees. It is semi-fluid, and semi-transparent, and in this condition is found abundantly between the bark and the wood of all trees in early spring; and thus separates those parts so as to permit the bundles of young wood to pass down from the leaves, and thus enable the tree to grow. It is under these conditions that the woodman strips the bark from trees which are to be cut down, since then it does not adhere to the wood.
The first step in the formation of any tissue from the formative fluid is the production of a solid structureless fabric called Elementary Membrane, and a modification of that fabric termed Elementary Fibre.
The structures which are produced from the above-mentioned “raw material” are very varied in appearance, and are called Cellular Tissues, to signify that they are made up of hollow cells. The spaces between the cells are called Intercellular Spaces, which are of vital importance, as they contain air. Woody fibre constitutes the mass of the stems of our forest trees. Its peculiar characteristic is that of great tenacity, and power of resistance, and for this its structure is admirably adapted: it consists of bundles of very narrow fibres, with tapering extremities, and is so placed from end to end, that the pointed ends overlap each other. Each fibre is very short, and the partitions which result from the apposition of the fibres, end to end, do not interfere with the circulation through them. The tube is not composed of simple thin membranes only; but in addition has a deposit within it, which, without filling the tube, adds very greatly to the strength of the fibre: an arrangement whereby the greatest strength and power of resistance and elasticity shall be obtained; and, at the same time, the functions of circulation uninterruptedly maintained. The strength is mainly due to the shortness of each fibre, the connection by opposite ends of many fibres, almost in one direct line, from the root upwards; and lastly, to the deposit on the inner side of the membrane. The uses of woody fibre are very varied and most important; it is the chief organ of circulation in all wooded plants, and, for this purpose, pervades the plant from the root to the branches. The current in this tissue is directed upwards from the shoot, through the stem to the leaves, and downwards from the leaves through the bark to the root. Thus, its current has a twofold tendency; the ascending and chief one being for the purpose of taking the raw, or what is called the common sap, from the ground to be digested in the leaves, and the descending being devoted to the removal from the leaves of the digested, or what is termed the proper sap, to be applied to the purposes of the tree, and also of the refuse matter to be carried to the roots, and thence thrown out into the soil as a noxious material. The proper sap differs considerably in different trees; it is always less liquid, and contains a much greater proportion of vegetable matter than the common sap. It is very probable that trees of the same kind produce proper sap of different qualities in different climates.
Woody Fibre may be considered the storehouse of the perfected secretions. It is well known that as trees advance in life, the wood assumes a darker colour, and more particularly that lying near to the centre of the stem. This is due to the deposit of the perfected juices in the woody fibre at that point; and where age has matured the tree, it is probable that the woody fibre so employed is no longer fitted for the circulation of the sap; and, also, that the perfected sap, when once deposited, does not again join in the general circulation. The dark colour of the heart of oak, as contrasted with oak of very recent growth, is an illustration of this fact, as is also the deep colour which is met with in ebony and rose-wood. Technically, the inner wood is called the heart-wood, and the outer or younger wood the sap-wood. Of these, the former contains little fluid, and no vegetable life, and, being the least liable to decay, is therefore the most perfect wood; the latter is soft and perishable in its nature, abounding in fermentable elements; thus affording the very food for worms, whose destructive inroads hasten its natural tendency to decay.
The proportion of sap-wood in different trees varies very much. Spanish chestnut has a very small proportion of sap-wood, oak has more, and fir a still larger proportion than oak; but the proportions vary according to the situation and soil, and according to the age at which they have been felled: for instance, the teak tree in Malabar, India, differs from teak in Anamalai, South India. This subject has been very fully treated by Mr. Patrick Williams, in his valuable work on Naval Timber.