GROUP II. BRYOPHYTA. 309 



GROUP II. 

 BRYOPHYTA (Muscinese). 



The plants forming this group, that is the Liverworts (Hepa- 

 ticae) and the Mosses (Musci), are characterised by the following 

 distinctive features. Their life-history presents a regular and well- 

 marked alternation of generations : the gametophyte is the more 

 conspicuous form, constituting " the plant " : the sporophyte is a 

 sporogontum, presenting indications of differentiation into root and 

 shoot, but not of the shoot into stem and leaves ; it never becomes 

 an independent individual, but remains attached to the game- 

 tophyte, from which it derives all or much of its nutriment. In 

 some of the Mosses there is an indication, in both the sporophyte 

 and the gametophyte, of a differentiation of vascular tissue. 



The GAMETOPHYTE. The germinating spore does not at once 

 give rise to what is known as the " Moss-plant," but produces an 

 embryonic body, the protonema, which consists generally of a 

 branched filament, but occasionally of a flat layer, of cells which 

 contain numerous chloroplastids. The protonema is generally in- 

 conspicuous and short-lived in the Hepaticse, whilst in the Musci 

 it is more amply developed and may, either wholly or in part, 

 persist from year to year. 



The "Moss-plant " is the adult sexual form. It does not possess 

 any true roots, but is attached to the soil either by unicellular 

 root-hairs (Hepaticse), or by multicellular protonematoid filaments 

 termed rhizoids (Musci). The body of the " Moss-plant " is essen- 

 tially a shoot, which is highly developed and specialised in con- 

 nexion with the functions which it performs the development of 

 the sexual reproductive organs and, in the case of the shoots 

 bearing female reproductive organs, the nourishment of the at- 

 tached sporophyte developed in consequence of fertilisation. The 

 adult shoot arises as a lateral (rarely terminal) bud on the proto- 

 nema : the protonema may give rise to a single shoot (Hepaticae) 

 or to several (generally in Musci). In the latter cases, the adult 

 shoots may become distinct " plants " by the complete or partial 

 dying away of the protonema. The symmetry of the shoot is, 

 almost uniformly, dorsiventral in the Hepaticse and radial in the 

 Musci. It is either thalloid, as in most Hepaticae ; or it is 

 differentiated into stem and leaf, as in the higher Hepaticae 

 (foliose Jungermanniaceae) and in the Musci. 



