HARDWOOD RECORD 



15 



Tree Growth and the Vhysics of Wood. 



A tree is a perennial woody plant, having a 

 single self-supporting stem or trunk, the 

 Avhole ranging above ten feet in height. 



Although nearly five hundred more or less 

 distinct species of tree growth thrive in this 

 <ountry as natives, and many others can be 

 successfully cultivated here, the bulk of the 

 wood used for general purposes is taken from 

 a comparatively small number of these many 

 and varied forms. According to government 

 statistics, the principal timbers of commerce 

 of the United States are known popularly as 

 pine, fir, oak, hickor}', ash, maple, walnut, 

 poplar, spruce, cedar and cypress. Where the 

 requisition is for size or quantity, rather than 

 for beauty of finish, the varieties of poplar, 

 gum and cottonwood are employed. Where a 

 handsome appearance is required, as in furni- 

 ture manufacture and decorative work, oak, 

 maple, walnut and ash figures show to be most 

 frequently used. Where hardness, uniformity 

 and close grain must be insured, as in imple- 



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ritnss SECTION EXOGENOUS STEM- 

 POPLAR. 



mcnt handles and in the manufacture of 

 countless novelties ana small articles, hickory 

 and rock elm are the most prominent woods. 



The great confusion which exists almost 

 universally regarding the proper classification 

 of nearly every kind of wood can be avoided 

 only by the use of the strict botanical name 

 for each variety. In the different lumber 

 markets and in many localities which produce 

 the same species, it is known by as many 

 different names, making it impossible to place 

 the tree without a careful examination and 

 botanical classification. Thus, on hearing the 

 term "ironwood" used in New York, "blue 

 beech" in Pennsylvania or "hornbeam" in 

 Maine, it might be impossible to tell whether 

 the Ciiri>inus caroliniana of one botanist, the 

 Ostriia ririjiniana of another, or the G-xuija- 

 c'Miii sanctum of still another was referred to. 

 One distinct species of pine is called in the 

 various markets and lumber camps of the 

 country by not less than thirty names. 



The usual botanical designation of a plant 

 consists of two terms; the first signifies genus 

 and the second species; thus, the ordinary 

 black walnut of commerce is known to scient- 



ists a.s Ju(jlans nigra. The first or generic 

 name applies to any one of the numerous 

 varieties in the group, while it is to the 

 second that we look for positive identification 

 of species. These botanical terms often differ 

 with authorities, so that it is customary to 

 suffix the name of the botanist making the 

 classification, as Jiiniperns monospcrma Sar- 

 gent. 



Snow's definition of wood is as follows: 

 ' ' Wood is made up of cell-structures, as, the 

 true fiber, which originates from several cells; 

 the tracheid, which originates from one; the 

 vessel, which is a short, wide tube joined 

 vertically end to end with others of its kind; 

 the pith-ray; the resin-duct, and others, all of 

 which are often popularly referred to as 

 fibers. The character and arrangement of 

 cell-structures differ with species. Wood is 

 hard, soft, light, heavy, tough, porous, elastic 

 or otherwise because of these differences. ' ' 



The qualities of wood vary greatly with 

 surroundings, climatic conditions, etc., and 

 are easily affected by various agents. Weight, 

 for instance, differs from one season, or even 

 day, to another, as water is taken up or 

 evaporated. Strength varies with grain, age, 

 and even atmospheric conditions. Figures 

 pertaining to the physical qualities of timber 

 cannot be too much relied upon, owing to 

 these varying tendencies. Statements and 

 statistics concerning certain specimens may 

 bo absolutely correct as regards the specimens 

 themselves, but should be applied with cau- 

 tion to the species in general. The differences 

 which exist in tree forms, due to age, to their 

 appearance in the forest, under cultivation, 

 etc., often make it a difficult matter to dis- 

 tinguish between the many varieties. 



Trees are divided into two great classes — 

 exogens and endogens — according to the way 

 in which new material or growth is added to 

 them. These divisions correspond to dicoty- 

 ledons and monocotyledons, respectively, which 

 classification is made according to whether 

 there are two or one seed-leaf. Exogenous 

 trunks are built out by layers or rings being 

 formed one upon the other. Among them are 

 nearly all the well-known timbers of com- 

 merce — the pines, maples, oaks, and others. 

 Endogenous trunks increase in diameter by 

 the interposition of new cellular and vascular 

 tissue irregularly among that already formed, 

 rather than by the formation of concentric 

 rings. While the growth of a tree in diameter 

 is by one of these two methods, it lengthens 

 by a sort of ' ' telescopic extension at the buds 

 or extremities," which in their turn attain the 

 size and strength of branches. 



A cross section of an exogenous tree shows 

 the stem to consist of pith, wood and bark. 

 New wood is porous and offers free passage 

 to the sap; hence its name, sapwood. As 

 annual ring upon annual ring forms about the 

 sapwood, it becomes compact and its tiny 

 passages fill with deposits or gums, its color 

 is altered, and the so-called heartwood results. 

 In some trees this process is slow, so that 



large sections of sapwood arc found, while in 

 others the change is rapid, and almost the 

 entire trunk appears to be heartwood. It is 

 in the latter that the qualities most valued in 

 construction are found — toughness, weight, 

 strength and durability, although heartwood 

 is not necessary to the life of the tree. It is 

 in the sapwood that vitality exists, but for 

 building purposes it is not nearly so valuable. 

 The pliability of sapwood, however, makes it 

 useful in cabinet and furniture construction. 



Wood varies according to the seasons in 

 which it is formed. These differences in 

 deposits mark the boundaries of the annual 

 or complete rings. In certain trees, the hick- 

 ory for instance, spring wood shows many 

 more pores than does the summer growth, and 

 in the pines even greater contrast is seen, the 

 spring and summer woods appearing as dis- 

 tinct bands. 



A cross section of an endogenous stem pre- 

 sents a dotted, pith-like appearance, due to 



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citoss sECTiiiN i:nihi(;knous stem — 



I'ALM. 



the fact that the new fibers intermingle with 

 the old and push outward irregularly througli 

 the porous tissue. Bark is not common to the 

 family. The bamboo, palm and yucca are 

 endogens. 



The wood of an endogenous tree is hardest 

 and most compact on the outside. The inside 

 may be either solid, as in the palm, or hollow, 

 as are some of the rapidly growing grasses — • 

 the bamboo notably. The hollow center is 

 due to the fact that the central pith grows 

 more slowly than the new outer tissue, so 

 that it is finally forced to disrupt and dis- 

 appears as a central core. Joints or knots 

 appear distinctly on the stem of the cane or 

 bamboo, and the intervening spaces show the 

 amount or length of annual growth. 



Endogenous stems are rarely cut into the 

 form of lumber, but are used in segments or 

 whole. The bamboo is useful for a variety 

 of purposes, especially maritime, and is made 

 into rafts, masts, yards, spears, pipes, fans 

 and boxes of all kinds. Most of the endogens 

 are herbs and grasses — the cornstalk, wheat, 

 rye, maize, sugar-cane, rattans and Joshua 

 tree all belong to this great tribe, in addi- 

 tion to those heretofore mentioned. 



