250 



HARDWICKE'S SCIENCE -GOSS IP. 



[Nov. 1, 1867. 



mosses of delicate texture, where it is persistent 

 during their whole life. But some mosses rarely 

 produce fruit ; yet it is necessary that their repro- 

 duction should be ensured, and we find prothallium 

 also developed from tubercles on the roots, from 

 gemmae or buds occurring on the leaves, or even from 

 the cell-tissue of leaves themselves ; while iu some 

 mosses a portion of the leaves become altered into 

 gemmae, and clustered in a head on the top of a 

 naked stalk called a pseudopodium, as in Tetraphis 

 pellucida and Aulacomnium (fig. 256). 



Fig. 236. Pseudopodium of Aulacomnium androgynum, 

 with one of the gemma?. 



The Roots. — These are slender fibrils, by which 

 the plants are attached to their place of growth— 

 the soil, crevices in the bark of trees, or rocks — and 

 consisting of a single series of cells, the septa be- 

 tween which are always oblique to the axis of the 

 filament. Adventitious radicles or rhiziuae of a 

 brown or purple colour also frequently occur on the 

 stein, 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 repeatedly branched. It is of the 

 same thickness throughout, for it grows only at the 

 apex, or is acrogenic, and is composed of dense 

 elongated cells, 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 

 refiexed, 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 

 Polytrichia, 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 con- 

 stitute the areolation, and afford characters of the 

 greatest importance in the diagnosis of species, 

 indeed used by some recent Bryologists, as Carl 

 Midler and Hampe, for the chief divisions in classi- 

 fication. 



In form, the cells are hexagonal, but varying to 

 quadrate, rhomboidal, or linear, according to the 

 density of their arrangement, and their surface may 

 be smooth, or covered with minute papilla?. They 

 contain granules of chlorophyl, which is often beau- 

 tifully distinct, and the cause of the fine green 

 colour, well seen in Bryum 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 

 their chlorophyl, those at the base are empty, 

 hyaline, and elongated ; in a few mosses the 

 chlorophyl is wanting, and hence they have a white 

 aspect, as in the family Leucobryaceae. 



Occasionally the basal wing of the leaf is occupied 

 by cells, which differ from the rest, being enlarged 

 or deeply coloured, and the presence or absence 

 of these alar cells has been conveniently used by 

 Prof. Schimper to divide the great genus Dicraiium 

 into two (fig. 170). When the cell ends join by hori- 

 zontal walls, they are termed Parenchymatous, and 

 in one form of these, the cell walls are thickened, 

 and the cell proper reduced to a mere point, producing 

 the dotted areolations of Grimmiaceoe and others 

 (figs. 257, 25S). When the cell ends are pointed, 



> » - 



Fig. 25". Areolation of Pottia 

 tnmcata. 



Fig. 253. Areolation of 

 Grimmia apocarpa. 



we have rhombic areolae, and these are termed 

 Prosenchymatous, as in Bryum (figs. 259, 260). I 

 must add that occasionally stipuliform organs occur 

 intermixed with the stem leaves, as in Hypnum 

 molluscum ; these are named Paraphyllia. 



An anomalous form of leaf occurs in the genus 

 Bissideus, in which it appears to be vertical, and 

 split into two laminae for a part of its length. This 

 split portion is, however, the true leaf, but the 

 nerve and one wing have taken upon themselves 



