How crops growA treatise on the chemical composition, structure, and life of the plant, for all students of agriculture .. . of the fibers, and arereadily seen in most kinds of woodwhen split lengthwise. They areespecially conspicuous in the oakand maple, and form what is com-monly known as the botanist terms them pith-raysor medullary rays. Fig. 51 exhibits a section of abit of wood of the Red Pine,(Pinus picea,) magnified 200 di-ameters. The section is madetangential to the stem and length-wise of the wood-cells, four ofwhich are in part represented, A /it cuts across the pi
How crops growA treatise on the chemical composition, structure, and life of the plant, for all students of agriculture .. . of the fibers, and arereadily seen in most kinds of woodwhen split lengthwise. They areespecially conspicuous in the oakand maple, and form what is com-monly known as the botanist terms them pith-raysor medullary rays. Fig. 51 exhibits a section of abit of wood of the Red Pine,(Pinus picea,) magnified 200 di-ameters. The section is madetangential to the stem and length-wise of the wood-cells, four ofwhich are in part represented, A /it cuts across the pith-rays, Mhosecell-structure and position in the wood are seen at m, n. Cambium of Exogens.—The growing part of the exog-enous stem is thus found between the wood and the bark,or rathey between the fully formed wood and the maturebark. There is, in fact, no definite limit where wood ceasesand bark begins, for they are connected by the cambial orformative tissue, from which, on the one hand, wood-fibers,and on the other, bast-fibers, or the tissues of the bark,rapidly develope. In the cambium, likewise, the pith-rays. Fig. 51. THE VEGETATIVE OEGANS OF PLANTS. 277 which connect the inner and outer parts of the stem, con-tinue their outward growth. In spring-time the new cells that form in the cambialregion are very delicate and easily broken. For this rea-son the rind or bark may be stripped from the wood with-out difficulty. In autumn these cells become thickenedand indurated, become, in fact, full-grown bast and wood-cells, BO that to peel the bark off smoothly is impossible. Minute Structure of Exogenous Stems.—^The accom-panying figure (52) will seive to convey an idea of the mi-nute structure of the elements of the exoarenous stem. It
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectagricul, bookyear1868
