THE 



121 



-cr 



The innermost series of cells undergo extensive changes. Each one usually 

 divides into two, which are known as the " Capitula" (c), and from these bud 

 out numerous branches which may become at once divided into many cells by a 

 series of transverse divisions ; or the branches may form secondary capitula, 

 which in turn develop several (usually three or four) of the long filaments (F). 

 In each cell of the filaments, which form a tangled mass filling the antheridium, 

 there is developed a single large spermatozoid (G, H). These arise mainly 

 from the nucleus of the sperm-cell by its becoming elongated and coiled, but 

 the two long cilia and part of the body of the spermatozoid arise from the 

 cytoplasm. 



When the antheridium is quite ripe, the shields separate, and expose the fila- 

 ments to the water, and the slender, spirally coiled spermatozoids escape through 

 a pore in the wall of the 

 sperm-cell. A 



Oogonium. The oogoni- 

 um, in Chara (Fig. 92), repre- 

 sents a leaflet springing from 

 the basal node of the anther- 

 idium. It also produces a 

 basal node, and internode. 

 The former consists of a cen- 

 tral cell and five peripheral 

 ones. The latter elongate and 

 form a covering about the 

 apical cell, which becomes the 

 oogonium proper. The five 

 elongated cells which surround 

 the oogonium become spirally 

 twisted, and from the upper 

 end of each is cut off a cell, 

 which with the others form 

 the five-celled crown at the 

 apex (Fig. 92, C). In the 

 Nitelleae a second crown-cell 

 is cut off from each of the long cells, so that the crown is composed of two 

 tiers of cells which are sometimes thrown off (Fig. 92, E). 



From the base of the oogonium in Chara a flattened cell (Fig. 92, C, x) is cut 

 off, and in Nitella two or three. The larger cell then becomes the egg-cell and 

 contains a very large nucleus, and is filled with large starch-granules and oil- 

 drops, which make it very opaque. The upper part, however, is comparatively 

 free from granular contents, and forms the receptive spot. 



FIG. 92. A-D, development of the oogonium in 

 Chara sp. A-C, longitudinal sections ; D, cross- 

 section (X 200). E, young oogonium of Nitella 

 sp. (X 200) ; o, egg-cell; cr, crown-cells. 



Fertilization. When ready for fertilization the long cells about 

 the oogonium separate somewhat below the crown, with a slight elon- 

 gation at this point. Five clefts are thus formed below the crown 

 through which the spermatozoids enter the space above the apex of 

 the oogonium. The wall of the latter becomes softened at the apex 

 so that the spermatozoid can penetrate into the egg, with whose nu- 

 cleus it fuses. The egg now becomes a resting-spore, and the inner 

 walls of the surrounding cells become hard and woody, and some- 

 times the walls also are silicified. As the fruit ripens, the chro- 

 matophores sometimes become red or yellow. Finally the outer 



