GROUP II. BRYOPHYTA : MUSCI. 335) 



presence of loose assimilatory tissue, rich in chloroplastids, the 

 intercellular spaces of which communicate with the outer air by 

 means of the stomata. 



The hypobasal cell undergoes relatively few divisions. In the 

 Sphaguacese it gives rise to a bulbous foot. In the Bryinese (e.g. 

 Qrthotrichum, Barbula, Atrichum where the hypobasal cell under- 

 goes a single division by a transverse wall) the true foot is 

 rudimentary, but it is functionally replaced (e.g. Phascum, Ephe- 

 merum, Polytrichum) by the dilated lower end of the seta which 

 constitutes a false foot. 



After fertilisation, the venter of the archegonium developes into 

 the calyptra which, for a time, keeps pace with the growth of 

 the contained embryo, but is eventually ruptured by the gradual 

 elongation of the seta. In Sphagnacese, and in some of the lower 

 Bryinese, the whole of the ruptured calyptra remains as a sheath, 

 the vaginula, round the base of the short seta ; in the higher 

 Bryinese the lower portion remains as the vaginula, whilst the 

 upper portion is raised up like a cap (still called calyptra) on the 

 top of the elongating sporogonium. The floor of the receptacle 

 (i.e. the apex of the sexual shoot) is also stimulated to growth, 

 forming in most cases a conical projection on which are borne the 

 paraphyses and the unfertilised archegonia, whilst in Sphagnacese 

 it elongates into the long pseudopodium (see p. 312). The perichse- 

 tial leaves also grow up round the lower part of the seta or of the 

 pseudopodium. 



The sporogonium, possessing, as it usually does, assimilatory 

 tissue and stomata, can assimilate the carbon dioxide of the air, 

 and can transpire actively. The supply of water necessary to 

 meet the loss by transpiration is obtained, together with salts 

 in solution, from the gainetophyte, being absorbed from it by the 

 true (hypobasal) or the false (epibasal) foot, and travels to the 

 capsule through the rudimentary xylem-tissue of the central strand 

 present in the seta of the higher forms. It is a point of consider- 

 able physiological interest that the absorption of water in the 

 first instance by the gainetophyte is apparently effected for the 

 most part by the leaves rather than by the rhizoids. 



The remarkable capacity for vegetative propagation manifested 

 by the gametophyte is shared by the sporophyte. It has been 

 ascertained that if portions of the capsule or of the seta, whilst 

 the cells are still living, be kept under favourable conditions, 

 the superficial cells will grow out into protonemal filaments. In 



