. Text-book of botany, morphological and physiological. Botany. FORMATION OF CELLS. formed on the side (Fig. 4, A, 2?), not at one end of the protoplasm-mass. The arrange- ment of the entire protoplasm of the cell is therefore entirely changed; the trans- verse becomes the longer diameter of the cell and of the plant arising from it. The material remains, as far as can be seen, the same, but its arrangement is different. This is the point of morphological importance, that every formation of a new cell depends essentially on a fresh arrangement of protoplasm already in existence. Hence the reju
. Text-book of botany, morphological and physiological. Botany. FORMATION OF CELLS. formed on the side (Fig. 4, A, 2?), not at one end of the protoplasm-mass. The arrange- ment of the entire protoplasm of the cell is therefore entirely changed; the trans- verse becomes the longer diameter of the cell and of the plant arising from it. The material remains, as far as can be seen, the same, but its arrangement is different. This is the point of morphological importance, that every formation of a new cell depends essentially on a fresh arrangement of protoplasm already in existence. Hence the rejuvenescence of a cell not only may but must be regarded morphologically as the formation of a new one! 2. Cell-formation by Conjugation.—The protoplasm of two or more cells coalesces to form one common protoplasm-mass, which surrounds itself with a cell-wall and becomes endowed with the other properties of a cell. To study this process, which presents many variations, we may take one of our commonest fila*- mentous Algae, Spirogyra longata (Figs. 5, 6). Each filament (Fig. 5) consists of a row of similar cylin- drical cells, each of which contains a protoplasm-sac; this encloses a relatively large quantity of cell-sap, in the midst of which hangs a nucleus, enveloped in a small mass of protoplasm, and attached to the sac by threads of the same substance; in the sac lies a spirally coiled chlorophyll-band, with thickenings (chlorophyll - granules) at intervals which contain starch-brains. The conjugation always takes place between opposite cells of two more or less parallel filaments. The first stage is the formation of lateral protuberances (Fig. 5, a), which continue to grow until they meet (b). The protoplasm of each of the two cells concerned then contracts1, detaches itself from the surrounding cell-wall, rounds itself into an ellipsoidal form, and contracts still more by expulsion of the water of the cell-sap. This may occur simultaneously in the two conjugating cells. Ne
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
