324 PART III. THE CLASSIFICATION OF PLANTS. 



GROUP II. 

 BEYOPHYTA (Muscinese). 



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

 ticse) 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," and does not possess 

 the power of reproducing itself asexually by gonidia, which is so 

 common among the Thallophyta : the sporophyte is a sporogonium, 

 presenting indications of differentiation into root and shoot, but 

 not of the shoot into stem and leaves ; it never becomes an inde- 

 pendent individual, but remains attached to the gametophyte, 

 from which it derives 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 is heteroblastic (see p. 14) in its development. 

 The germinating spore does not at once give rise to what is known 

 as the " Moss-plant," but produces an embryonic body, the proto- 

 nema, which consists generally of a branched filament, but occasion- 

 ally of a flat layer, of cells which contain numerous chloroplastids. 

 The protonema is generally inconspicuous 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 (Hepaticae), or by rnulticellular 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 (Hepaticoe) 

 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 Hepaticse ; or it is 



