. Wood and forest . UCTUKE OF WOOD. 39 but not over I3// in diameter. A Jarge knot is sound, and over 1>4in diameter. A spilce knot is one sawn in a lengthwise position. Adead, or, loose knot is one not firml) held in place \>y growth orposition. (4) Pith. At thecenter or axis of thetree is the pith ormedulla, Fig. 34. Inevery bud, that is, atthe apex of everj stemand branch, the pith isthe growing part; butas the stem lengthensand becomes overgrownby successive layers ofwood the pith loses itsvital function. It doesnot grow with theplant except at thebuds. It varies inthickness, being v
. Wood and forest . UCTUKE OF WOOD. 39 but not over I3// in diameter. A Jarge knot is sound, and over 1>4in diameter. A spilce knot is one sawn in a lengthwise position. Adead, or, loose knot is one not firml) held in place \>y growth orposition. (4) Pith. At thecenter or axis of thetree is the pith ormedulla, Fig. 34. Inevery bud, that is, atthe apex of everj stemand branch, the pith isthe growing part; butas the stem lengthensand becomes overgrownby successive layers ofwood the pith loses itsvital function. It doesnot grow with theplant except at thebuds. It varies inthickness, being verysmall, — hardly moiethan 1/16, in cedarand larch,—and sosmall in oak as to beliardly discernible; andwhat there is of itturns hard and herbs and shoots itis i-elatively large, , p. 1-5, in a three-year old shoot of el-der, for exa7nple, be-ing as wide as the wood. In elder, moreover, it dies early and pul-verizes, leaving the stem hollow. Its function is one of only tem-porary value to the Fiy. 34. Section Tbru the Trunk- of a Seven YearOld Tree, Sliowinj^ Relation of Branches to MainStem. A, B, two branches which were killed aftera few years growth bv shadin!^--, and which havebeen overgrown by the annual rin^rs of wood; C, alimb which lived four years, then died and brokeoff near the stem, leaving- the part to the left ofXY a sound knot, and the part to the rif^ht adead knot, which unless rotlinj^ sets in, wouldin time be entirely covered by the growing- trunk;D, a branch that has remained alive and has in-creased in size like the main stem; P, P, pith ofboth stem and limb. 40 WOOD AND FOREST. THE STRUCTURE OF WOOD. ReFEKENCES : * Roth, Forest Bull. No. 10, pp. 11- Bitting, Wood Craft, 5: 7G, 106, 23. 144, 172, (June-Sept. 1900). Boulger, pp. Ward, pp. 1-38. Sickles, pp. 11-20. Encyc. Brit., 11th Ed., -Plants, Pinchot, Forest Bull. No. 24, I, pp. p. 741. 11-24. Strasburger, pp. 120-144 and Part Keelev, pp. .514-517. II, Sec. II. Curtis, pp.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectforests, bookyear1912
