1868.] BRAITHWAITE ORGANIZATION OF MOSSES. 465 



attached to their place of growth — the soil, crevices in the bark of 

 trees, or rocks — and consist of a single series of cells, the septa 

 between which are always oblique to the axis of the filament. 

 Adventitious radicles or rhizina3 of a brown or purple colour also 

 frequently occur on the stem, uniting the plants into a dense 

 matted tuft, and like a sponge conveying water to every portion. 



The stem. — Often simple, and sometimes so short as to appear 

 wanting, it is in the terminal fruited mosses repeatedly forked, 

 for on the cessation of each annual growth, a lateral bud is thrown 

 off at the apex, producing an innovation or secondary stem ; in 

 the lateral fruited mosses, however, the stem is truly and repeat- 

 edly branched. It is of the same thickness throughout, for it 

 grows only at the apex, or is acrogenic, and is composed of dense 

 elongated ceils, which thus render it firm and tough, those of the 

 outer layer being often richly coloured. 



The leaves. — These are always sessile and simple, their form 

 usually ovate or lanceolate, but varying in every degree between 

 orbicular and awl-shaped. They are inserted spirally on the 

 stem, though sometimes appearing to be distichous, or in two 

 opposite rows ; they may be erect, or spreading, or reflexed, or 

 curled, and again they may be secund, or all turned to one side. 

 The margin may be simple, or have a thickened border, entire or 

 toothed, plane or wavy, involute or revolute. 



The leaves may also be nerveless, but usually there is a central 

 nerve, which may be short, or reach the apex, or be excurrent in 

 a point, or long hair, and some mosses have two nerves. In the 

 Polytricha, the nerve consists of a number of erect lamellae, on 

 its upper surface. The leaves consist of a single, sometimes of a 

 double, or triple stratum of cells, the form and arrangement of 

 which constitute the areolation, and afford characters of the 

 greatest importance in the diagnosis of species, indeed used by 

 some recent Bryologists, as. Carl Miiller and Hampe, for the 

 chief divisions in classification. 



In form, the cells are hexagonal, but varying to quadrate, 

 rohmboidal, or linear, according to the density of their arrange- 

 ment, and their surface may be smooth, or covered with minute 

 papillae. They contain granules of chlorophyl, which is often 

 beautifully distinct, and the cause of the fine green colour, well 

 seen in Brijum capillare, while in others it is expended on the 

 growth of the cell, or the thickening of its walls, and thus in 

 many mosses, while the cells in the upper part of the leaf retain 



