(cost of Del. $1,178,000) is so great that a general idea may be obtained by which to judge of the durability of timber used before and after thorough seasoning. I judge that the loss to the Government in using unseasoned timber during six years from 1861 was at least $ 20,000,000."

Incomplete as these statistics are they give us a partial idea of the magnitude of the loss, which we sustain by decay, and they fully warrant our devising means for arresting it.

One of the chief difficulties which presents itself, when we resort to chemical processes to effect the preservation of wood, lies in its very complicated structure. Being the product of vital processes and also the individual in which these processes are taking place, a tree necessarily contains very many different chemical substances arranged in a complicated manner. It is to the character of the constituent substances and the manner of their arrangement that wood owes the properties which render it so well suited to the purposes to which it is applied.

A brief description of the structure of a tree and the way in which it is formed will more clearly explain these difficulties. If we examine a section of the stem of a tree we observe that it consists; 1st, of the pith or its remains, at the centre; 2nd, of the wood surrounding the pith; and, 3rd, of the bark.

In Fig. 1 is represented a section both vertical and horizontal of a branch of a tree, two years old, as it appears in December. The portion included in the lines marked A is of the first year's growth; those marked B indicate the wood of the second year; while those marked C inclose the three layers of bark; D represents the pith of loose cellular tissue; E represents the pith rays or silver grain of hard cellular tissue connecting the pith with the green or middle layer of bark, which consists wholly of cellular tissue; F marks the outer or corky layer of the bark, which is composed of dry, dead cells, which are formed of consecutive layers from the outer portion of the living green layer; G is the green layer of cellular tissue; H shows the liber or inner bark, made up of cellular tissue penetrated by long bast cells, arranged parallel with the axis of growth; I represents the place of the cambium or growing layer of organizable material which descends from the leaves between the liber and the sap wood during the period of growth; K is a woody fibre, which gives strength to the stem and through which the crude sap rises; L indicates the vessels or ducts, with various markings, such as dots, rings and spirals, which are formed most abundant

ly in the spring and usually contain no fluid. They convey gases and aqueous vapors, and it may be that a large proportion of all the water ascending from the roots to the leaves passes through them as vapor; M is the layer of spiral vessels or ducts, which always inclose the pith and in the young shoot extend into the leaves and unite them to the pith during its life, which ceases with the first season.

Though the assertion has given rise to much discussion it seems now to be well determined that a circulatory system exists in vegetables. For convenience it is divided into the vascular circulation and the horizontal or cellular circulation. In the first the sap from the roots passes up through the woody fibre and the elaborated sap or cambium passes down between the liber and the sap wood. In the second the fluids pass between the pith and the bark. The food for the growth of the tree is secured by the roots and the leaves. The roots absorb water and the nitrogenous and mineral substances which the tree requires. The leaves store up carbon from the decomposition of carbonic acid in the numerous stomatae with which they are provided. From these various substances the several constituents of the tree are formed and by the circulatory system they are conveyed to the part of the individual where they are to perform their functions. Thus we see that while the tree lives, in a healthy state, by means of its roots and leaves, it holds communion with the earth, water, and air, and that the fluids, juices and deposits depend for their movement upon the presence and action of these parts. When this communication is interrupted by drought or exhaustion of the soil, by the stripping of the bark or the felling of the tree, growth ceases. The circulation still coutinues however, but waste a of tissue begins, decomposition sets in, and the tree becomes the prey of fungoid growth. If however, after felling, we lop off the top of the tree, the vascular circulation ceases, and, if we remove the burk, cellular circulation stops. If now the tree is exposed to dry air at a moderate temperature, all vital processes are arrested and the wood is for the while preserved. Especially is this so if the sap wood is cut away and the pith is laid open.

From this sketch we realize how very complex the physical structure of the tree is. A narration of but a portion of the constituent substances will show that its chemical structure is still more diversified. In all plants we find woody fibre or cellulose, and this is covered with incrusting substances formed from the decay of the cells. The following substances are also found in quantities varying with the season and the locality, the species and the age of the plant. They are the constit

uents of the sap such as albumenoidal substances, starch, grape sugar, cane sugar, gum, tannic acid, coloring matters, pectose, resins, and volatile oils and the ordinary mineral constituents of plants, &c.

From the composition and structure of the healthy material our discussion naturally turns to the consideration of the manner in which the decay (Eremacausis) takes place and of the conditions most favorable to its progress. When wood in a moist state is ex posed to air it undergoes decomposition; a species of fermentation is occasioned by the nitrogenized constituents, in consequence of which oxygen is absorbed, carbonic dioxide and water are exhaled, and the wood crumbles down into a blackish brown vegetable mold called humus, ulmine or geine. This decay occurs most rapidly in young, spongy wood, which admits the air most freely and at the same time contains a proportion, ately larger quantity of the albuminous substance, than the harder and older portions. The decomposition of these albuminous constituents favors the growth of lichens and fungi and encourages the ravages of insects, to which the albuminous portions in particular afford nutriment. Pure woody fibre by itself, is only very slightly affected by the destructive influences of weather as we see in cotton, linen, paper and other materials, formed from nearly pure cellulose. The decay arises wholly from the presence of the substances in the wood that are foreign to the woody fibre, but are present in the juices of the wood while growing, and consist chiefly of albuminous matter, which, when decaying, causes the destruction of the other constituents of the wood also. Since resinous woods resist the action of damp and moisture for a long time, they are quite lasting; next in respect to durability follow such kinds of wood as are very hard and compact and contain some substance, which like tannic acid, resists decay.

The conditions which obtain then are these; a limited supply of air, a moist atmosphere, and a moderate temperature. Change either of these conditions and decomposition ceases. You will recall that these conditions air, moisture and heat are the very same as were shown by our eminent associate, Dr. Gihon, to exercise so baneful an effect upon the health of those who live in ships. Remove the moist atmosphere and while the health of the inhabitants is benefited the destruction which assists in polluting the air is delayed.

Mr. Finchau, formerly Principal Builder to Her Majesty's dockyard, at Chatham, tried an experiment to show that the presence of all these conditions was essential to decay. He bored a hole in a perfectly sound timber in an old oak ship. The admission of air to the central part of

་་་ ་་་'' 'རོཝཱ