A practical course in botany : with especial reference to its bearings on agriculture, economics, and sanitation . THE STEM 121. t rrr Fig. 138. — Diagram to showthe common method of sawing alog. The circles represent ringsof annual growth : R, R, diam-eter of the log ; r, r, r and t, t, I,boards cut perpendicular to it,givdng for the two or three cen-tral ones radial, for the others,tangential, cuts. The waste por-tions are the slabs and edg-ings, shown in the dark seg-ments at R, R, and the smalltriangular blocks, e, c, e. radius of a log. Repeat the geo- ^ t rrr metrical principle upon whic
A practical course in botany : with especial reference to its bearings on agriculture, economics, and sanitation . THE STEM 121. t rrr Fig. 138. — Diagram to showthe common method of sawing alog. The circles represent ringsof annual growth : R, R, diam-eter of the log ; r, r, r and t, t, I,boards cut perpendicular to it,givdng for the two or three cen-tral ones radial, for the others,tangential, cuts. The waste por-tions are the slabs and edg-ings, shown in the dark seg-ments at R, R, and the smalltriangular blocks, e, c, e. radius of a log. Repeat the geo- ^ t rrr metrical principle upon which such a cut is described as tangential. It passes through the medullary rays and the annual rings diagonally (Fig. 136), and is the cheapest way of cutting timber, since the entire log is made into planks and there is no waste except the slabs and edgings, as shown in Fig. 138. The cut ends of the medullary rays appear on the surface as small lines or slits (Fig. 137), and give to this kind of plank its peculiar grain-ing. The wavy or watered appearance of the annual rings (Figs. 133, 136, 140, 141), so often seen in ch
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