. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. 14 DEVELOPMENT OF CELLS. Fig. 44. cells are also produced by the division of the primordial utricle, which gradually folds iawards about the middle, forming an annular constriction, and ultimately a complete separation of the utricle into two parts. Each of these afterwards becomes covered by a permanent cell-wall. This is seen in Palmella (fig. 44). Henfrey has supported this view by observations made on the hairs of Tradescantia and of Achimenes grandiflora, in which
. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. 14 DEVELOPMENT OF CELLS. Fig. 44. cells are also produced by the division of the primordial utricle, which gradually folds iawards about the middle, forming an annular constriction, and ultimately a complete separation of the utricle into two parts. Each of these afterwards becomes covered by a permanent cell-wall. This is seen in Palmella (fig. 44). Henfrey has supported this view by observations made on the hairs of Tradescantia and of Achimenes grandiflora, in which he has traced the gradual formation of a septum, linger traces in Algse the development of new cells by a fissiparous (fissus, split, and pario, I produce) or merismatic (,u,i§ie//,6g, division) separation of the old ones into two or four divisions, in the same way as occurs in pollen. In some of the most simple plants, multi- plication takes place by a sort of sprouting of new cells from old ones, like buds from a stalk: the portion thus shooting out being afterwards separated from the parent plant by a partition. This is seen in Torula, the yeast plant. The various theories of cell-development (cytogenesis) may be re- duced to the following : 1. Formation of cells in protoplasm, existing in the interior of a cell; 2. Formation of cells in protoplasm, not contained in a cell, but isolated; 3. Formation of cells by merismatic division of the primordial utricle, or protoplasmic lining of the cell; 4. Formation of I- C cells by a process of budding. Cells are also formed by what has been called Conjugation, or by the union of two cells, which by their mutual action give origin to a third. This is particularly seen in some of the lower Algse, such as Zygnema (fig. 45). The formation of cells goes on with great rapidity, especially in the case of fungi. From an approxi- mative calculation, it is found that in Bovista gigantea 20,000 new cells are formed every minute. Ward 1 ^p5&a
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