MESSRS. BETHELL AND CO.’S TIMBER PRESERVING APPARATUS 136
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.