1042. The organic basis of all plants whatever is vegetable tissue, of which their elementary organs consist. When this tissue is first formed it is called cellulose, and is composed of twenty-four parts of carbon, ten of oxygen, and twenty of hydrogen; 'but its chemical nature is rapidly altered by the addition of azote and other matters, and especially by an increase in the relative proportion of carbon.' (Lindl. Elements of Botany, p. 1.) 'Tissue occurs in the form of the cellular, the woody, the vascular, the pitted, and the laticiferous, the different modifications of which constitute the elementary organs.' (Ibid. p. 2.) Cellular tissue, or parenchym, consists of a number of vesicles, each distinct in itself, but 'cohering with the vesicle with which it is in contact,' so that 'the apparently simple membrane which divides two contiguous cells is, in fact, double.' The pulp, or parenchyma of leaves, the medulla, or pith of wood, the medullary rays, and all similar portions of plants, are compound cellular tissue. Woody tissue, or pleurenchym, 'consists of elongated tubes tapering to each end,' and it is 'distinguished by its cylindrical form, great length, extreme fineness, and toughness.' Woody tissue is found in the wood, in the liber of the bark, in the veins of the leaves, and in various parts of the footstalks, stem, Pitted tissue, or bothrenchym, appears to be only a form of cellular tissue, and it consists either of 'short cylindrical cells placed end to end, opening into each other, and forming continuous tubes ; or of long tubular cells. Its sides are marked with pits, resembling dots.' (Elem. of Bot. p. 5.) This tissue forms the porous part of woods. Vascular tissue, or trachenchym, 'consists of very thin-sided cylinders, tapering to each end, and having a fibre or fibres spirally generated in their inside.' (Ibid. p. 7.) Spiral vessels conveying air, and ducts conveying sap, are the ordinary forms of this tissue. Laticiferous tissue, or cinenchym, 'consists of uninterrupted anastomosing tubes, having thick un-marked sides.' These vessels are largest in plants having milky juice, and smallest in those whose juice is transparent. (See Lindl. Introd. to Botany, 4th edit. (1848), vol. i. p. 91.)
