Botany / by J.D. Hooker.

  • Joseph Dalton Hooker
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: Botany / by J.D. Hooker. Source: Wellcome Collection.

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    form of bundles which traverse the parenchyma, as the veins (or nerves) of the leaves, and are called fibro-vascular bundles. IV.—THE NATURE OF THE CELL, AND GROWTH OF CELL-TISSUE. io. To understand how plants grow, and how such products as sugar, starch, oils, and resins are formed in them, it is necessary to examine further cellular tissue; for it is by the addition of cell to cell that plants grow, and by chemical changes taking place within the cell, that the above-named and other sub- stances are formed. i n. The cell consists of a membrane (cell-wall) and its contents (cell-contents). The cell-wall is a thin (rarely thick) transparent bag of dead matter called cellulose. This bag contains when young a viscid granular substance endowed with life and some- times exhibiting motion, called protoplasm. Cellulose is composed of oxygen, hydrogen, and carbon; proto- plasm cf these together with nitrogen and sulphur. 12. When cells are very young they are smaller in size, the cell-wall is thinner, and they are completely filled with the protoplasm; a darker rounded portion of this is generally to be noticed in them and is called the nucleus. As the cells grow in size their cavity becomes larger than the mass of protoplasm which originally filled it. The cell-wall is always lined by a layer of protoplasm, but in the interior of the cell cavities are formed in the protoplasm which are filled with a watery fluid called the cell-sap. At a later period, the protoplasm is reduced to a thin