358 PAET III. THE CLASSIFICATION OF PLANTS. 



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 secreting 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. 233) ; the base of the 

 stalk is dilated in some cases (e.g. Andreaea). 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. 235). 



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 lacustre, 

 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, arciicum, 

 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 

 less well-marked histological differentiation. The outer portion 

 generally consists of one or more layers of elongated prosenchy- 

 matous cells, with thickened walls which are yellow or brown, 

 forming the cortex which passes by gradual transition into thin- 

 walled parenchymatous ground-tissue ; in the subterranean shoots 

 of the Polytrichaceag, however, the cortex is parenchymatous and 

 thin- walled, whilst the central tissue is thick- walled. 



In many species a central strand, lying in the longitudinal axis 

 of the stem, can be distinguished, the structure of which presents 

 two principal varieties ; it may be simple, consisting of a group of 

 thin- walled tracheides, destitute of protoplasmic cell-contents (e.g. 

 species of Mnium, Meesia longiseta, Archidium alternifolium) ; or it 



