. A textbook of botany for colleges and universities ... Botany. 724 ECOLOGY bsog^. glucose; in addition they have remarkable fila- mentous nuclei. In some conifers, reservoirs filled with resin occur in the bark, as in the balsam blisters of the fir {Abies halsamea). The role of duct se- cretions. — Probably the contentsof resin and mu- cilage ducts are chiefly waste products. Since such substances usually cannot be excreted ex- ternally, it is presumably advantageous that they accumulate in reservoirs outside the regions of nutritive activity. Even if resins and similar ex- cretions are wast
. A textbook of botany for colleges and universities ... Botany. 724 ECOLOGY bsog^. glucose; in addition they have remarkable fila- mentous nuclei. In some conifers, reservoirs filled with resin occur in the bark, as in the balsam blisters of the fir {Abies halsamea). The role of duct se- cretions. — Probably the contentsof resin and mu- cilage ducts are chiefly waste products. Since such substances usually cannot be excreted ex- ternally, it is presumably advantageous that they accumulate in reservoirs outside the regions of nutritive activity. Even if resins and similar ex- cretions are waste prod- ucts, they may have subsidiary advantages; for example, they may preserve the wood from decay, as in the conifers, thus facilitating longevity. Perhaps resins and gums are of advantage in healing wounds and in checking loss of water, as in the pines and cherries, where they exude copiously at the injured places. Incisions cause not only the flow of resin, but also in some cases the development of accessory ducts. Fig. 1039. — A cross section of an edge of the needle- like leaf of the Austrian pine {Pinus Laricio), showing the epidermis (c) with its much thickened walls, the outer part (<r) being cutinized and the inner part («') not; X, hypodermalsclerenchymatous tissue; /, chloren- chyma with infolded cell walls, the outermost cells (p) having these walls perpendicular to the surface, suggest- ing palisades; .*, stoma with guard cells (^), subsidiary cells (6), stomata! cavity (i), and pit (0); r, resin duct, the secretory cells (y) being surrounded by a scleren- chymatous cylinder {x')\ highly magnified. Tannins and other hark excretions. — Among the commoner excretions found in bark (as in the oak) are tannins, which are astringent glucosids. In Sanibucus the tannin is contained in special sacs, twenty millimeters long or thereabouts, but usually the tannin-containing cells are in rows and often near the vascular tract. Brown and red colors in the bark inte
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
