BRYOPHYTES 115 



It is introduced here partly to illustrate the possible effect of changed conditions 

 upon structure, but chiefly to illustrate another synthetic form. 



Gametophyte. — The gametophyte develops first as a mass of cells {primary 

 tubercle). From the superficial cells of the primary tubercle extensively branch- 

 ing filaments arise, which represent the protonema of the true mosses, as contrasted 

 with the thallus of Sphagnum and the liverworts. The branches of the filament 

 that enter the rock crevices are rhizoids ; those that remain exposed to the light 

 are green and may assume any one of three forms dependent upon conditions : 

 (1) they may remain filamentous; (2) they may form flat plates; or (3) they 

 may form cylindrical masses. The leafy branch may arise from any of these three 

 forms. Arising from filaments, it resembles a true moss ; arising from a plate 

 of cells, it resembles Sphagnum. 



Sex organs. — The antheridia occur at the apex of a special branch, involving 

 the apical cell ; this resembles true mosses and not Sphagnum. In form, however, 

 the antheridium is globular and long-stalked, resembling Sphagnum and not the 

 true mosses. The archegonia also occur at the apex of a special branch, this 

 character being common to leafy liverworts, sphagnums, and true mosses. 



Sporophyte. — The sporophyte presents the great peculiarities of the group. 

 The sporogenous tissue is cut off from the endothecium as the outermost layer of 

 cells, a feature resembling true mosses but not Sphagnum ; but the sporogenous 

 tissue caps the columella like a dome, a feature resembling Sphagnum but not true 

 mosses. A pseudopodium develops instead of a seta, as in Sphagnum. The 

 dehiscence of the capsule is very peculiar, for instead of the operculum of other 

 mosses, there are four vertical slits that do not reach the apex, recalling the four 

 valves of the capsule of Jungermanniales. In fact one of the Jungermanniales 

 (Symphyogyna) has just this dehiscence by means of four vertical slits. 



Conclusions. — The combination of characters may be summarized as follows : 

 the gametophyte is either thallose, as in Sphagnum, or partly filamentous, as in 

 true mosses ; the antheridia are terminal, as in true mosses, but long-stalked and 

 globular, as in Sphagnum ; the sporogenous tissue is derived from the endothecium, 

 as in true mosses, but caps the columella, as in Sphagnum and Anthoceros ; the 

 capsule dehisces by four slits or valves, as in Jungermanniales, and not by an 

 operculum, as in other mosses ; a pseudopodium is developed, which is a feature 

 of Sphagnum, but not of true mosses. 



(3) Bryales 



General character. — This is the great assemblage of mosses, dis- 

 tinguished from all others as true mosses. It includes the most highly 

 organized bryophytes, and is their most representative group, but it 

 seems to be a closed line; that is, it has given rise to no higher groups. 

 Although a vast group, it is so uniform in general structure that a single 

 account will suffice. 



Gametophyte. — The gametophyte is a branching filament {proto- 

 nema, fig. 251), which is the equivalent of the thallus of Sphagnum 



