20 HANDBOOK OF BRITISH MOSSES. 



from each other, so that some of them fall off, and an aperture 

 is left for the admission of the sperm atozoids, which in moist 

 weather soon find their way to the aperture, and travel down 

 the channel to the basal cell, when ready for impregnation. 



After impregnation has taken place, cell division com- 

 mences in this cell, and is continued till an oblong or subglo- 

 bose cellular mass is formed within the archegon, and distinct 

 from it, stretching its walls, and in most cases lifted upwards 

 by the elongation of a distinct stalk, till the archegon splits at 

 the base, or more rarely in the centre forming above a little 

 hood or veil to the body called a ' calyptra/ or veil, and after 

 dehiscence, leaving behind a little sheath, called the 'vaginula/ 

 from the centre of which the fruitstalk grows, and which is in 

 fact the foundation or extreme base of the archegon and con- 

 fluent with the axis, as in the course of development, should 

 the archegon have been at first lateral, it becomes terminal. 



According to the mode of dehiscence, the vaginula is more 

 or less modified, and in many cases it is so incorporated with 

 the axis, that the axis itself seems hollowed out, and the ex- 

 ternal surface of the vaginula is rough with abortive arche- 

 gons and paraphyses. In general only a single archegon in 

 each group proceeds to perfection, though doubtless several 

 may be impregnated, exactly as in a bunch of pear blossoms, 

 though several may be impregnated and the ovules swell for a 

 time, some one or more individuals will take the lead, abstract- 

 ing the nourishment from the rest, so that their progress is ar- 

 rested, and they ultimately become detached at the base of the 

 peduncle. In some cases, as in Bryum roseum, several arche- 

 gons are perfected. In Sphagnum the vaginula is lifted up on 

 a cylindrical hyaline stalk, the sporangium itself being almost 

 sessile, and the same structure obtains in Andreaa. 



The veil itself is more or less persistent, sometimes falling 



