GROUP III. PTERIDOPHYTA. 377 



tissue ; the short neck consists of a single layer of cells in four 

 rows. . The mature archegonium contains, in the venter, the 

 female cell (oosphere). 



The archegonium is developed from a single superficial cell of 

 the prothallium. This cell divides transversely into two, an upper 

 and a lower ; the former, by growth and division, forms the neck 

 of the 'archegonium ; the lower cell projects into the developing 

 neck, and the projecting portion becomes cut off, constituting the 

 neck- canal- cell which sometimes divides again into two (Maratti- 

 acese, Lycopodium) ; the remainder, now termed the central cell of the 

 archegonium, divides transversely into two unequal parts, the upper 

 and smaller being the ventral canal-cell, the lower and larger being 

 the oosphere. As the archegonium becomes mature, the canal- cells 

 become mucilaginous, the neck opens by the separation of the cells 

 at the apex, and the archegonium is ready for fertilisation. 



The male cell, or spermatozoid, is a naked motile cell ; it is a 

 spirally coiled filament, pointed at the anterior end which bears 

 the cilia, becoming thicker towards the opposite end ; the cilia 

 are numerous in Filicince (incl. Isoetes) and Equisetinae ; two in 

 Lycopodina3. 



Each spermatozoid is developed singly in a mother-cell in the 

 antheridium ; it consists of kinoplasm with a nucleus (see p. 116). 

 The whole of the contents of the mother-cell are not, however, 

 devoted to the spermatozoid : a portion remains unused, and is 

 discharged together with the spermatozoid, to which it adheres 

 for a time as a protoplasmic vesicle containing, amongst other 

 constituents, a portion of the nuclear substance of the mother-cell 

 (see Fig. 266). 



The female cell, or oosphere, is a naked spherical cell lying in the 

 venter of the archegonium. Its development is described above. 



Fertilisation is effected by the entrance of spermatozoids into 

 the open neck of the mature archegonium, and the subsequent 

 fusion of one of them with the oosphere. When, as is usually the 

 case, numerous prothallia are developed near together on the 

 ground, and become wetted by rain or dew, the ripe antheridia 

 burst and set free the spermatozoids which, swimming actively in 

 the water, are attracted to the mature archegonia by means of an 

 acid excretion which is discharged from the neck of the arche- 

 gonium when it opens. The effect of fertilisation on the oosphere 

 is that it at once surrounds itself with a cell-wall becoming the 

 oospore, and then begins to develope into the young sporophyte. 



