GROUP II. BKYOPHYTA. 



327 



central row constitute the neck- canal-cells. At maturity the ter- 

 minal cells, lid-cells, of the neck separate ; the neck-canal-cells 

 and the ventral canal-cell become mucilaginous and disorganised, 

 so that the oosphere is placed in communication with the exterior 

 by the canal of the neck. Fertilisation takes place when the 

 plants are more or less covered with water from rain or dew. 

 Then the antheridia dehisce, the spermatozoids are set free, and, 

 since the male and female organs are at no great distance, they, 

 swimming by 

 means of their 

 cilia, come into 

 the neighbour- 

 hood of the arche- 

 gonia ; they are 

 attracted to enter 

 the necks of 

 archegonia by 

 the escaping mu- 

 cilage formed by 

 the disorganisa- 

 tion of the canal- 

 cells, which con- 

 tains an organic 

 acid which has 

 been shown to be 

 especially attrac- 

 tive to spermato- 

 zoids. One of 

 the entering 

 spermatozoids 

 travels down the 

 canal to the 

 oosphere, which 

 it penetrates, the 

 nucleus of the 

 spermatozoid fusing with that of the oosphere. Fertilisation is 

 now complete ; the fertilised oosphere surrounds itself with a cell- 

 wall and becomes the oospore, which begins to divide and to 

 develope into the sporophyte. 



The effect of fertilisation is not confined to the oosphere. The 

 adjacent tissue of the shoot is stimulated to growth, and in some 



FIG. 235, Marchantia polymorpha. A Young ; B mature, but 

 unfertilised, archegonium. C Fertilised archegonium, with 

 dividing oospore. fc' Xeck-canal-cells ; fc" ventral canal-cell ; 

 o oosphere ; pr perigynium. ( x 540 : after Strasburger.) 



