. A textbook of botany for colleges and universities ... Botany. Fig. 1027. — A diagrammatic cross section of a carnation stem {Dianthus Caryophylltis), showing the develop- ment of a mechanical cylinder (m) out- side the vascular tract (v); c, c', cortical parenchyma; p, central pith. gram per square millimeter, some of the strongest bast has within its limits of elasticity a tensile strength of twelve to twenty-five kilograms per square millimeter, the higher figure being twice that of wrought iron and about equal to that of German steel; however, the breaking point of steel is much beyond t
. A textbook of botany for colleges and universities ... Botany. Fig. 1027. — A diagrammatic cross section of a carnation stem {Dianthus Caryophylltis), showing the develop- ment of a mechanical cylinder (m) out- side the vascular tract (v); c, c', cortical parenchyma; p, central pith. gram per square millimeter, some of the strongest bast has within its limits of elasticity a tensile strength of twelve to twenty-five kilograms per square millimeter, the higher figure being twice that of wrought iron and about equal to that of German steel; however, the breaking point of steel is much beyond that of bast. Bast differs widely from the metals in having a considerable degree of elastic elongation, and is itself ex- ceeded in this respect by the me- chanical strands of lichens, those of Usnea being capable of elongating sixty to one hundred per cent (see fig. 1113). Bast is considerably stronger when desiccated than when it contains moisture, though it is more elastic in the latter condition; ligni- fication usually decreases the tensile strength. The great tensile strength of bast is due to the amount and quality of the wall thickening, to the dovetailing of the prosenchymatic cells, and probably, also, to a spiral arrangement of the wall micellae. The fact that the limit of elas- ticity is so near the breaking point is not disadvantageous, since any elongation of bast beyond the limit of elasticity would be harmful. Collenchyma is almost as strong as bast, though it has a lower limit of elastic elongation. Having the power of growth elongation, it is espe- cially suited to growing Fig. 102S. — A diagrammatic cross section of the erect aerial stem of Juncus balticits littoralis, showing an interrupted mechanical cylinder, composed of alternating outer {or} and inner (z) fibrovas- cular bundles, in which a bast cylinder (fe) surrounds the vas- cular tract iy); note that the bast is more strongly developed out- ward than inward; c, cortex; a, large central
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
