WOOD and molars ; the latter are rootless, with fla crowns surrounded by enamel, there being a deep furrow down the inside of the upper am outside of the lower ones ; the whole numbe of teeth is 24 ; the body of the atlas remain permanently cartilaginous, the ribs are 15 o* 16 pairs, the humerus has an opening between the condyles and the inner one perforated, am the patella is absent ; there is a short ceecun and vermiform appendage. It is 2 or 8 ft long, plump, with a thick coat of long, grayish brown, woolly hair; head large, wide, flat and rabbit-like, with upper lip cleft, and smal eyes and ears; legs short and nearly equal, and the feet five-toed, all except the small in- ner one of the hind feet with long claws ; tail half an inch, nearly naked. The animal walks on the soles, which are broad and naked. It is nocturnal and slow-moving, living in holes among the rocks or in burrows dug by itself; the food consists of grass and roets ; it is easily domesticated, and has three or four young at u 703 "Wombat (Phascolomys wombat). birth. In the mountainous districts near Port Jackson its flesh is preferred to that of all other animals of Australia. Eemains of a fossil spe- cies have been found ' in the caves at Welling- ton valley, Australia. WOOD (A. S. wudu), the substance forming the body of the trunk and branches of a tree. The stems of flowering plants are made up of cells of two kinds ; the soft parts consist of thin and but little elongated cells, which to- gether form cellular tissue, and running through these are elongated tough and fibre-like cells forming woody tissue. In stems of only one season's duration, the proportion of woody tis- sue is small, and these are called herbaceous, and -the plants herbs. In stems which last from year to year the woody tissue largely preponderates over the cellular, and such stems furnish the substance known as wood. The characters of cellular and woody tissue are given under PLANT, and in that article will also be found an account of the manner of the growth and annual increase of stems, and mat- ters relating to their structure which have a direct relation to their value and utility as wood. The stems of endogens, while they are 841 VOL. xvi. 45 often of great utility in the countries producing them (see PALM), form no appreciable portion tne wood of commerce, and are but little u f d in temperate climates. Small quantities of Palmyra, porcupine, and speckled woods, trom the stems of the cocoanut and other palms, are employed by the makers of ornamental cabinet work, usually in the form of veneers, ine great class of exogenous plants furnishes most of the material known as wood ; in these the woody tissue is arranged in a circle around a central pith, and the stem increases in diame- ter by the formation of an annual layer upon the outside of the old wood ; the character of these annual layers, and the manner in which the woody tissue is interpenetrated by plates of cellular tissue, the medullary rays, greatly affect the physical properties of the wood. In chemical composition the different kinds of wood vary greatly ; the basis of the wood cells is the same as that of those forming cellular tissue, the principle cellulose (Cj a H 20 Oio), iden- tical in composition with starch, dextrine, and other principles, and but little different from the sugars. But the cells soon become thick- ened by the deposit upon their interior of a substance which renders them harder and thicker ; this incrusting material was formerly regarded as a distinct principle, to which the name lignine was given, but it is now regarded as a mixture of different substances, which on account of the difficulty of separating them from one another, and from cellulose, have not been analyzed ; these, according to their solubility in or relations to chemical reagents, have received the names lignose, lignone, lig- nine, and lignireose. Besides these, under the collective name of lignine, various resins, col- oring matters, and principles peculiar to par- ticular genera and families of plants, are depos- ited in the cells, as well as the earthy matters that appear in the ash .when wood is burned ; some of these deposits constitute the chief val- ue of particular kinds of wood, such as those used in dyeing, or to afford medicinal extracts. In many stems the change produced by the filling up of the cells is very marked, the older wood being much darker and harder; this is called heart wood, and the newer tissues, in which the change has not taken place, are called sap wood. In some cases the heart wood does not become colored, and its cells are but little
- hickened, as in the white pine, poplar, and
tulip tree, technically known as white timber or white woods. The heart wood has ceased ,o take any part in the -vegetative processes, being practically dead, and is of no use to he tree except by mechanically strengthening he trunk ; hence it is not rare to find trees in good health from which the centre has been amoved by decay. Trees are usually felled in winter, when vegetation is at rest, though it ias been asserted that if they are felled when n full growth, and the bark removed, the dry- ng is more thorough. The wood, at whatever ime the tree may be cut, contains a large
