. A class-book of botany; designed for colleges, academies, and other seminaries ... illustrated by a flora of the northern, middle, and western states; particularly of the United States north of the capitol, lat. 38 3/4 o. Botany; Plants -- United States; Plants -- Canada. ALBURNUM AND DURAMEN. 79 number of layers, if counted at the base, will correctly indicate the age of the tree. 202. Each woody layer is composed of ligneous librc, vasi- form tissue, and ducts (33,/"). The fust gives strength and solid- ity to the trunk, and determines the direction of the cleavage. a. The ducts are a
. A class-book of botany; designed for colleges, academies, and other seminaries ... illustrated by a flora of the northern, middle, and western states; particularly of the United States north of the capitol, lat. 38 3/4 o. Botany; Plants -- United States; Plants -- Canada. ALBURNUM AND DURAMEN. 79 number of layers, if counted at the base, will correctly indicate the age of the tree. 202. Each woody layer is composed of ligneous librc, vasi- form tissue, and ducts (33,/"). The fust gives strength and solid- ity to the trunk, and determines the direction of the cleavage. a. The ducts are always first formed and lie in the inner part next the centre, while the fibres are produced towards the end of the season, and are deposited in the outer parts of the zone. The former are distinguished by the large size of their open ends, while the woody fibres are more minute and compact. This cir- cumstance renders the limits of each layer distinctly perceptible in a cross section of the FIG. 26. — Sections of wood ; 1, 2, 3, horizontal, 4, 5, vertical. 1, Exogenous stem of one years growth ; a, pith, b, bark, c, medullary rays, rf, woody bundles of fibre and vessels; 2, stem of three years' growth, a, pith, e, bark, 6, c, rf, successive annual layers ; 4, a, pith, b, spiral vessels of the medullary sheath, c, doited ducts, d, woody fibre, e, bark ; 3, Endogen- ous stem, exhibitiiig the bundles of woody fibre, spiral vessels, and ducts, irregularly disposed in the cellular tissue ; 5, a, cellular tissue, 6, spiral vessels on inner side of c, dotted ducts, d, woody fibre on the exterior side. 6, Laticiferous vessels of the bark. 203. The outer and more recent portion of the layers constitutes the albur- num {albus, white), or sap-wood. This is usually of a softer structure and lighter color than the rest of the wood, and it is through the vessels of these layers alone, that the sap ascends. The interior layers of the alburnum gradually harden by the deposition of sol
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Keywords: ., bookcentury1800, bookdecade1840, bookpublisher, booksubjectbotany
