~ Te ass asaya SEZ FIG. 8 THE PROGRESSIVE GROWTH OF A TREE 15 A tree grows in diameter each year by the addition of a cone of wood which never increases in height after being formed. Compare with Fig.7. The age of the trunk is shown at various heights (44 years at the ground, 6 years near the top, corresponding to the number of rings in cross section)
16 AMERICAN MUSEUM GUIDE LEAFLETS FIG.9.CROSSSECTIONOFCHESTNUT Showingtheporous compact“summerwood” oh I oy eet perian ie!
oy ee ie had ” WADE 4 ti Be Os bo A 1 1% ax * J & ~ 3 ze “spring wood” and more noted for their narrow sapwood are locust, mulberry, Osage orange (Fig. 6), chestnut and larch.
Also in the wood of each cylinder or ring, there may be a differentiation in color and often in structure, that part of the cylinder which grows rapidly in the spring proving light in color and perhaps porous (spring wood) (Figs. 9 and 10). In fact, it is difficult to count the annual rings in birches, hornbeams, maples, poplars and willows, trees in which so little summer wood is made, that the spring wood of one year appears to adjoin the similar spring wood of the next year. We speak of the beginnings and additions of wood as evlinders, but, in truth, they are cones, aS a consideration of Figs. 7 and 8 will prove. <A cut through the central part ofa log so that the saw practically cuts through a radius of each cone will produce a board with its surface showing wood bands or lines relatively parallel (Figs. 11 and 13; radial or quartered cut of a a pyet t * 3:
roe, ie =.
5 CROSS SECTION OF DOUGLAS SPRUCE Indicating variation of spring and summer wood
TREES AND FORESTRY 17 FIG.12,COMMONMETHODOF FIG. Il. ONE METHOD OF QUARTER-SAWING SAWING TIMBER Quartered boards warp and split less than No quartered lumber results, tangential cuts of lumber because cut in the with the exception of afew boards direction of the pith rays. Compare with Figs. in the middle. There is waste in 13, 18 and 20 any method of sawing but charcoalblastfurnacesandchemical plants may convert bark, limbs, edgings and even sawdust into somevaluableproduct Radial Cut < .
Tangential Cut ’ ’ SS SS SSK Ss y MAA SG, ~~ Be FIG.13.RADIALANDTANGENTIALCUTSOFLUMBER > Boards cut from the central part of a log (and so at right angles to the wood rings and in the direction of the pith rays) produce radial, rift, or quartered lumber; other boards (tangent and oblique to the wood rings and more or less at right angles to the pith rays) give tangential, common, or bastard cuts of lumber. Compare with Figs. 11 and 20 FIG.14.BIRD'SEYEMAPLE Occasionally there is a tree in which the wood cylinders have fluted walls. Cutting through these fluted walls produces the ‘“‘bird’seye’’ marks on the boards
1S AMERICAN MUSEUM GUIDE LEAFLETS lumber). In a cut downward through a log some distance out! from the center, the saw continually strikes and cuts through the sloping walls of wood cones and the resulting board shows in its midline wood bands appearing as concentric angles or U-shaped figures (Figs. 12 and 13, tangential or bastard cut of lumber). ‘The U-shaped marks may be the result also of irregularity in the growth of the tree due to the effects of sun, prevailing wind or other external agency. Occasionally the wood cylinders for some unknown reason have fluted walls, in which case it is easy to see how a board gains the appearance called “bird’s eve,” illustrated in hard maple (Fig. 14). FIG.15.BLACKASHBURL Irregularity of the wood cylinders in burls or knots causes the unusual and often verybeautifuleffectsseeninburlveneers
TREES AND FORESTRY ir irs yD) SHS eo ) SDD D)DD))DIDODIDYDIB DYDD ND AD PILILTL] AVIDIALT DDD) )) ND From the leaf the food substances pass upward to the Luds, downward to the cambium and to the tips of the roots to supply all living parts with material for growth. DDD DSSS DD PDD DD Fe inp BID D DDD) VIII al FIG. 16.
It passes from the roots through change there, through the inner bark 19 Lhe chlorophyll of the leaf under the tnfluence of sunlight changes the water trom the roots and carbon dioxide from the air into starch-like products, later. convertead into netrogenous food SUBSTANCES. Db 33535:3)0)0)0)0)009)) ) LD) WWD); = The food from the root passes upward to the leaves throughthewood(sapwood), A gn an em!
Pet --- Wood F¥4-4----Inner Bark a (Bast) er:
Baye 7} 23 r~:
(ie ee Tnorgantc food substances, ¢.e. water carrying soluble mineral substances, enter at the roots (by osmosis through the root hairs ). DIAGRAM SHOWING COURSE OF THE SAP the wood to the leaves, and after its chemical (bast) to all growing parts
20 AMERICAN MUSEUM GUIDE LEAFLETS Irregularity of the wood cylinders in “burls,” overgrown knots and excrescences occasionally found on various trees, causes the unusual and often very beautiful effects seen in burl veneers (Fig. 15). It is the work of these various tissues in codperation for the tree’s maintenance as an individual that is of most interest. Water containing lime, potash and other minerals in solution, is taken up from the soil through the roots. This food cannot be used directly for growth by the tree any more than it could be by man. It is sent upward through the sapwood to the leaves of the tree. A tree may be girdled, that is, cut to the cambium, and also may be hollow through the whole extent of its heartwood, yet it will live for some time if there is continuous sapwood Ligh = Upper surface of leaf ——— Bascoeenss carbon aioride Innerbark oe, O ast) sD NG pene MONDiaatvitA DOOM — FIG. 17. ACTIVITIES GOING ON IN THE “CELLS” AND AIR SPACES OF A LEAF (1). Under the sun’s heat, water is continually evaporating from the leaf. A tree must lift several thousands of Ibs. of water to the leaves to get 1 lb. of mineral matter in solution in the sap. The greater part of this water is evaporated from the leaves. A birch tree gives off 700-1000 Ibs. of water daily; a single oak sends off into the air 130 tons of water annually (2). Carbon dioxide is absorbed continually in daylight by the leaf to make possible the starch-forming process, W hile free oxygen is at the same time given off as a waste product from this same process. This absorption of carbon dioxide and outpouring of oxygen makes one explanation of the fact that park and street trees increase the healthfulness of a city
TREES AND FORESTRY 21 from root to leaves. The living green substance (chlorophyll) of the leaves under the influence of sunlight breaks apart the hydrogen and oxygen, elements in this water gained from the roots, and at the same time separates the carbon and oxygen, elements in carbon dioxide gained from the air, and recombines the three, hydrogen, oxygen and carbon, to make various starch-like products. This chemical work of green plants, defying man’s efforts to imitate, creates food for animal life on the globe and is, in fact, the only source of that food. Later, the starch is changed to complex substances, largely because of the addition of nitrogen, and passes through the inner bark (bast) of the trunk, upward to give food to the growing buds, downward to supply the living cambium throughout its length with material for a new wood layer, and to give nourishment to the living tips of the roots (Fig. 16).
These plant activities, mechanical and chemical, are not fully understood. Osmosis or the passage of liquids through an organic membrane explains the entrance of water carrying soluble substances into the roots; and since in osmosis the movement is more rapid in the direction of the stronger solution, which in this case is within the roots, the continual passage of water into the roots must create considerable pressure upward. ‘This root pressure accounts in some degree for the rise of water in the trunk. Root pressure in birch trees will lift water in the tree trunk to a height of 84.7 feet. A second force acting to carry the current upward through the sapwood is probably capillarity (the force which causes rise of a liquid through any porous substance). A third force is the strong attraction naturaily existing between particles of wood and particles of water. A fourth is certainly the continual and often rapid evaporation of water from the tree’s enormous leaf surface which lies spread out under the heat of the sun (Fig. 17).
Other structures of the trunk, complicating an understanding of the appearance of lumber, are short, thin plates made of a substance like the pith, arranged radially and vertically through the wood but irregularly with reference to one another (Fig. 18). These plates, called pith rays, show as radial lines in a cross-section of a log (see upper section, Figs. 19 and 20). ‘They produce what is known as the silver grain of lumber, inconspicuous short lines on the surface of tangential boards because the plates are cut through their length and thickness, but often conspicuous in quartered Jumber where, cut through length and width, the plates are sometimes exposed for two or more inches on the board’s surface (see lower section, Figs. 19 and 20). The pith rays in different species of trees differ to such an extent that, like the variations of spring and summer wood, they serve to identify different kinds of wood. In oaks the rays are long and
22 AMERICAN MUSEUM GUIDE LEAFLETS PithRay as exposed by radial cut (The Pith Rays produce the Silver grain of the wood Pith Ray as seen in tangential cut FIG.18RELATIVEPOSITIONOFPITHRAYSANDWOODRINGS In a radial cut, the pith rays may show as broad bands (silver grain); in a tangential cut, they appear only as short lines. Compare with Figs. 19 and 20 FIG.19.OAKWOODSHOWINGPITHRAYS Narrow radiating lines in cross section, broad silvery bands in the quartered wood. Compare with Figs. 18 and 20