260 



PART IV. CLASSIFICATION. 



oospore by clothing itself with a proper wall, but also to cause the neigh- 

 bouring cells to grow round the oogonium and form a compact cellular 

 investment for it. Surrounded by this investment, the oospore falls to 

 the bottom of the water, as the plant dies down, and undergoes a period 

 of quiescence. On germination it grows, splitting the investment, and 

 divides to form a small multicellular body, the existence of which shortly 

 comes to an end by the escape of the whole of the protoplasmic contents 

 of all the cells as zoospores, one from each cell (Fig. 148 6'). 



Series V. CHAROIDE.E. The forms included in this series constitute but 

 a single order, the Characese. 



Order I. Characeae. The stem is distinctly segmented into nodes and 

 internodes, the nodes being marked by the whorls of leaves which they 

 bear. It consists of a longitudinal series of elongated cylindrical cells, 

 each of which constitutes an internode, separated from each other by 

 transverse plates of small cells which are the nodes. In Chara, there is, 



in addition, a cortex consist- 

 ing of rows of cells, sometimes 

 spirally twisted, produced by 

 a growth of the peripheral 

 cells of each node, both up- 

 wards and downwards, over 

 the internodes above and 

 below it. 



All the cells contain small 

 discoid chloroplastids which 

 lie imbedded in the proto- 

 plasm immediately beneath 

 the cell-wall. The more in- 

 ternal portion of the proto- 

 plasmic layer shows the 

 movement known as cyclosis ; 

 the central portion of the 

 cell-cavity, when the cell is 

 fully grown, is occupied by a 

 large vacuole filled with cell-sap. Each cell contains a single nucleus 

 when young; but the long internodal cells, when old, are found to 

 contain many nuclei produced by the fragmentation of the original 

 nucleus. 



The growth in length of the stem is unlimited, and is effected by means 

 of a hemispherical apical cell (Fig. 149). This cell undergoes repeated 

 division, a series of segments being cut off by transverse walls ; after a 

 segment has been cut off, the apical cell regains its normal size by 

 growth, then another segment is cut off, followed by renewed growth, and 

 so on. Each segment is immediately divided into two cells by a trans- 

 verse wall ; of these two cells the upper, in all cases, becomes a node, 

 dividing by vertical walls into the small cells, central and peripheral, of 

 which the node consists ; the lower, in all cases, becomes an internode ; it 

 does not divide, but simply grows in length. In Chara the young peri- 



FIG. U9. Diagram of growing-point of stem of 

 Chara fragilis (x500, after Sachs): a apical cell; 

 segment lately cut off ; n 1 n 2 n 3 successive nodes ; 

 in 1 in 2 in 3 successive internodes ; I leaves ; c cortical 

 cells growing down over in 3 from n 3 . 



