54 



BRITISH CHAROPHYTA. 



the spiral-cells are abruptly narrowed on their inner 

 side, leaving a cavity (Fig. 23 i, ii). Below this the 

 spiral-cells become tumid, leaving only a narrow 

 channel between them, leading to a second cavity 

 situated immediately above the oosphere (Fig. 23 ii). 

 The upper part of the spiral-cells lengthens, forming 

 a neck above the oosphere and under the coronula, 

 in the process of which the outer layer of the cell- 

 membrane splits transversely, leaving a jagged edge 



in 



FIG. 23. Process of fertilisation, i, ii, iii. Upper part of oogonium 

 of Chara vulgaris. iv. Oogonium of Nitella tenuissima. i. Half- 

 matured unfertilised oogonium showing upper and lower cavities 

 formed by development of coronula and enveloping cells, ii. Fully 

 matured unfertilised oogonium showing tumid growth at the head 

 of enveloping cells, and transverse fracture of membrane caused by 

 their extended growth, iii. Antherozoids penetrating interstices 

 formed by contracted terminations of spiral cells, and reaching 

 oospore through upper and lower cavities within, iv. Similar pro- 

 cesses in development of oogonium of Nitella (after De Bary). 



above and below (Fig. 23 iii). The apex of each of 

 these spiral-cells becomes slightly narrowed, leaving 

 between them a triangular space forming an aperture, 

 admitting to the upper cavity already referred to. 

 The aperture and cavity are filled with a colourless, 

 soft, viscous jelly to which antherozoids from neigh- 



