木材科学与工程专业英语

木材科学与工程专业英语内容摘要：

a result of rise in temperature are less significant in wood construction（木建筑） than they are in construction utilizing metal structural members. When heated, wood expands（膨胀） across the grain（纹理） as much as or more than metals, but only little in the longitudinal direction（纵向） , which is important in construction. Moreover, in wood, increase in dimensions with rise in temperature is frequently balanced to a considerable degree by shrinkage（收缩） caused by drying, with a corresponding increase in strength. There is no such pensating effect in metal structural members, which expand and lose strength progressively when heated. . Ⅴ . Knowledge of wood and better use / 木材知识与木材合理利用 Certain characteristics of wood are sometimes cited as detrimental to its use for particular purposes. However, when its properties are well understood, these supposed disadvantages may be minimized and in some cases even turned to advantage. For instance, the essentially tapered cylindrical shape（尖削柱状） of the tree trunk causes some losses in sawing straightgrained（直纹理） , rectangular lumber from logs, but this very shape of trunk（树干） offers a maximum stress resistance for a minimum of material used. 6 We may use wood with intelligence only if we understand wood. Chapter 2 Tree Stem And Its Growth / 树干与树干的生长  Ⅰ . The plant origin of wood / 木材来源于植物  Ⅱ . Parts of a tree / 树木的各个部分  Ⅲ . How a tree grows / 树木的生长  Ⅳ . Orientation of the tissues in a young tree stem (twig) / 幼树杆中各种木材组织的起源  Ⅴ . Bark structure / 树皮的构造  Ⅰ . The plant origin of wood / 木材来源于植物 Wood is plant origin. Not all plants, however, possess woody stems, and not all that do possess woody stems produce timber（木材） suitable for use as an industrial material. The following criteria serve to distinguish woody from nonwoody plants: （木本植物） must be vascular plants（维管植物）。 ., they must possess specialized conducting tissues（输导组织） consisting of xylem (木质部 ) and phloem (韧皮部 ). The xylem is lignified（木质化） and is the wood of the mature plant. Plants devoid of vascular tissue（维管组织） cannot produce wood. st be perennial plants（多年生植物）。 ., they must live for a number of years. be classed as woody plants because their stems die back to the ground each autumn, the roots persisting through the winter and producing a new stem the following spring. Some plants possess persistent creeping stems and hence fall into the category of woody plants, even though they appear to be herbaceous（草本的） . all the mercially important timber trees, exhibit secondary thickening（次生加厚）。 ., they have a means of thickening their stems by subsequent growth in diameter, not traceable to terminal growing points（顶端生长点） . This is achieved through the activities of a growing layers, called cambium（形成层） , which is situated just outside the last formed layer of wood and beneath the inner bark (phloem)。 new wood and new phloem are thus produced yearly and are developed between the previously formed wood and bark. In this manner, in the case of trees, the trunk eventually attains a diameter of sufficient size to be converted into lumber or other useful products. Ⅱ . Parts of a tree / 树木的各个部分 A tree has been defined as a perennial, vascular, woody plant（多年生具有维管组织的木本植物） which attains a height at least of 20 feet and usually (not always) has a single, selfsupporting stem. Although trees, like other vascular plants, exhibit a surprising range of variation in size, form, and structure and are, in reality, plex anisms, they are 7 constructed according to a simple, uniform plan. The plant body consists of a continuous cylindrical axis, which bears lateral appendages. The main portion of the axis above ground is the stem, trunk, or bole。 this divides successively into limbs（树丫） , branches（树枝） , and branchlets（小枝） , often in a manner characteristic for the tree species. The remainder of the axis is embedded in the earth。 like the portion above ground, it divides again and again, and forms the root system（树根系统） . The stem provides mechanical support for the crown（树冠） , serves as an avenue for conduction between the crown and the roots, and, on occasion, may store appreciable amounts of reserve food. Roots, in contrast, are ans of anchorage and support, which in addition perform the functions of absorption by means of root hairs or mycorhiza（菌根） , of conduction, and of storage. Both roots and stems exhibit radial symmetry when cut transversely ., the various parts are arranged around a mon center. Trees are different from the higher animals in which bilateral (right and left) symmetry is the rule. Ⅲ . How a tree grows / 树木的生长 Wood on a mercial scale is obtained only from trees of some maturity. Since the processes of growth in length and in thickness in trees are identical with those that take place in the production of seedlings from seeds, and trees from seedlings, a discussion of the manner in which growth proceeds in the mature tree will serve the purpose of this text. A tree, as previously noted, consists of a branched cylindrical axis to which appendages of various sorts are attached. The trunk and muchbranched crown pose the portions of this above the ground。 below the surface of the ground, the axis divides more or less abruptly into a wide spreading root system, which in size and bulk pares favorably with the crown. Until the tree attains maturity, enlargement of the crown and root system proceeds at a fairly rapid pace, in later years undoubtedly more sluggishly. But elongation, at least in some parts of the crown and root system, never stops during successive growing seasons, ., as long as the tree lives. Elongation of the branches on cylindrical axis is traceable to apical growing points（顶端生长点） , and to these alone. Through growth proceeding in these, the axis increases in length, branc。