File:Text-book of structural and physiological botany (1877) (14773143701).jpg

Identifier: textbookofstruct00thom (find matches)
Title: Text-book of structural and physiological botany
Year: 1877 (1870s)
Authors: Thomé, Otto Wilhelm, 1840- Bennett, Alfred William, 1833-1902
Subjects: Plant physiology
Publisher: New York : J. Wiley & sons
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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of cork formed of thin-walled cells parallelto the circumference of the stem, (x 370.) is firmer, less elastic, and more leathery than true cork.When it is several layers in thickness, thick and thin-walled layers often alternate (Fig. 67), causing frequently apeeling off, as in the birch and cherry; in the beech andsilver fir, on the contrary, the periderm does not peel off. Cark is the true healing-tissue of plants, and as such is of greatimportance. In the fresh surfaces of wounds, the uppermost layers ofcells as a rule dry up, while in the tissue beneath them, still full of sap,new cells are formed which are the origin of the cork. A very goodexample of the importance of this production of cork is afforded by thecochineal-cactus. This plant is multiplied by cuttings, which woulddecay at once if they were set in the ground with the surfaces of thewound fresh. The shoots which are intended as cuttings are thereforefirst laid for about four weeks in a dry place exposed to the sun, in
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Fig. 67.—Transverse section through the innermost layer of the bark of the oak ; p p layer ofperiderm consisting of thick-walled cells filled with a homogeneous red ma^s ; / / paren-chymatous cells with starch-grains ; st parenchymatous cells with moderately thickened,st^ with strongly thickened walls ; b^ bast-vessels orsieve-tubes ; pybast-tubes ; b paren-chyma and bast-vessels ; kr a large parenchymatous cell containing a crystal ; ^- a peri-, derm-like tissue, (x 440.) 46 Stritctural and Physiological Botany, order that a cork-tissue may be formed, which closes the wound andprevents the decay of the cutting. ^ Larger wounds, as, for instance, when branches are cut off, are oftenclosed by the formation of elevated cushion-shaped masses of cells, notconsisting entirely of cork-tissue, which are fresh formed over the wholesurface of the wound. Such a tissue is called an overgrowth, and isseen especially in the beech, silver fir, and lime (Fig. 68). Of a similar

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