. Introduction to structural and systematic botany, and vegetable physiology. Botany. hy lengthening throughout every part; which is a characteristic feature of the stem. 132. The root, however, does not grow from its very apex, as is commonly stated; but the new formation (by continued multiplica- tion of cells, 33) takes place just behind the apex (Fig. 135), which consists of an obtusely conical mass of older cells. As these wear away or perish, they are replaced by the layer beneath; and so the advancing point of the root consists, as inspection plainly shows, of older and denser tissue th
. Introduction to structural and systematic botany, and vegetable physiology. Botany. hy lengthening throughout every part; which is a characteristic feature of the stem. 132. The root, however, does not grow from its very apex, as is commonly stated; but the new formation (by continued multiplica- tion of cells, 33) takes place just behind the apex (Fig. 135), which consists of an obtusely conical mass of older cells. As these wear away or perish, they are replaced by the layer beneath; and so the advancing point of the root consists, as inspection plainly shows, of older and denser tissue than the portion just behind it. The point of every branch of the root is capped in the same way. It follows that the so-called spongioles or spongelets of the roots, or enlarged tips of delicate forming tissue, have no ex- istence. Not only are there no special organs of this sort, but absorption evidently does not take place, to any considerable extent, through .the rather firm tissue of the very point itself 133. Absorption by Roots. As the surface of the root, like every part of a plant, consists of closed cells, it is evident that the moist- ure it so largely takes in must iss be imbibed through the walls of the cells, by endosmose (40); and that the whole surface of a fresh root will take part in ab- sorption. The newer the root, however, the more actively does it absorb, the cells then having thinner walls. As they become older, the superficial layer of cells thicken their walls and form a kind of skin, or epider- mis (69), tlirough which absorp- tion does not take place so free- ly. Roots accordingly absorb mostly by their fresh tips and the adjacent parts; and these are constantly renewed by growth, and. FIG. 135. The tip of the root of a seedling Maple (Fig. 106), magnified : o, the place where growth is mainly taking place, by cell-multiplication : 6, the original tip of the radicle. FIG. 136, 137. Portions of the surface of the same, highly magnified, showing the natu
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Keywords: ., bookauthorgra, bookcentury1800, bookdecade1850, booksubjectbotany
