GROUP ii. BRYOPHYTA: MUSCI. 335 



The Sexual Organs are borne in groups (rarely singly) at the 

 apex either of the main shoots (acrocarpous), or of lateral branches 

 (pleurocarpous), surrounded by involucral leaves, each group with 

 its involucre constituting a receptacle. Generally speaking the 

 growth of the shoot or branch ceases with the development of the 

 sexual organs, the apical cell itself giving rise to an antheridium 

 or an archegonium ; but in some male receptacles (e.g. Polytrichacese 

 and some other Bryinese, also Sphagnum) the apical cell persists as 

 such ; consequently the elongation of the shoot or branch is not 

 necessarily arrested by the development of the antheridia, and 

 appears to grow through the receptacle. 



Among the sexual organs there are usually present multicellular 

 hairs, termed paraphyses: they are often filamentous, but in some 

 cases (e.g. male receptacle of Funaria) the terminal cells are large 

 and rounded ; they are hyaline, or coloured red or yellow, some- 

 times brownish, and the cells frequently contain chloroplastids. 

 They are more numerous and more highly developed in the male 

 than in the female receptacles ; they are rarely absent in plants 

 which grow in dry situations, but frequently in those forms which 

 grow in water or in damp places. Their function seems to be 

 that of sesreting water to prevent the drying-up of the sexual 

 organs. 



The antheridia are generally club-shaped (spherical in Sphag- 

 num), and are shortly stalked (see Fig. 192). The antheridia 

 generally open at the apex to allow the spermatozoids to escape. 

 The archegonia are stalked ; the neck is long, and the venter is 

 but slightly dilated (Fig. 195). 



The distribution of the sexual organs is various. The plant 

 may be monoecious (i.e. may bear both kinds of sexual organs), or 

 it may be dioecious : amongst the monoecious forms may be distin- 

 guished those which are monoclinous, that is, which have both 

 male and female organs in the same receptacle (e.g. Bryum la- 

 custre, cuspidatum, etc.), the archegonia being in the middle ; and 

 those which are diclinous, that is, which bear the male and female 

 organs in distinct receptacles : sometimes (e.g. Bryum pendulum, 

 arctic um, etc.) the plants are heteroclinous or polygamous, that is, 

 some receptacles are hermaphrodite, whilst others are unisexual. 

 In the dioecious species the male plant is usually the smaller, and 

 is short-lived. In some species the plants are sometimes monoecious 

 (either monoclinous or diclinous) and sometimes dioecious. 



The Structure of the Adult Shoot. The stem presents more or 



