THE CELLS OF MOSSES. 5 



Splacknunis, Fimaria, and Bryiims are admirably adapted for this 

 purpose, while the first-named give the opportunity of studying 

 some of the physical changes in the cell-walls of these exquisitely- 

 curious and beautiful leaf-cells. 



The Sphagmims also present examples of intercelhdar spaces or 

 empty cells, which in a normal state of growth are filled with 

 water, but when dry with air, to which is owing the glossy appear- 

 ance of the whole family and the genus Leucobryuvi^ when they 

 are not in a moist condition. 



Paretichymatoiis cells, or those which are more or less cubical, 

 and where the length does not exceed the breadth, are found in 

 the leaves of Fisidens, Tortti/a, Polytrichwn, Orthotric/ium, Pottia, 

 and at the apices and bases of the leaves of many other mosses. 

 While Prosenchy))iato2is cells, or those in which the cells are 

 always much longer than they are broad, the extremities tapering 

 more or less, and overlapping each other, are found in the leaves 

 of Bryum, Sphagnum, Hypmmi, Dicramcm, and Ca7npylopus. 

 Indeed, the/^rw of the cells that exist in Mosses is so varied — as 

 Schimper points out in the Introduction to his Moss Flora — that of 

 itself it might afford a vast field of intellectual work to the ardent 

 observer. Thus, as regards the cells of the leaves alone, there is 

 very great variety. In Orthotrichum the cells are hexagonal, with 

 the centre, as it were, pierced or punched out. In Pottia and 

 others the cells are quadrangular and hexagonal. In Bryum and 

 Rhyncostegiu7n they are rhomboid. In many other HypjiacecE they 

 are hexagonal-linear. In the true Hypnums they are linear, often 

 extremely long, vermicular, and flexuous linear ; while they are 

 sinuous and linear in Grimmia and Andrecea. 



Mosses, also, afford excellent specimens for examining simple 

 epidermal tissue, and that in variety and different degrees of per- 

 fection. It is most highly developed in the Sporogonium or fruit and 

 its seta or stalk, the cells being small and comparatively firm and 

 strong/as is also the case in the stems of Hyptium, Bryum, Tortula, 

 Dicranu77i, Ca7/ipylopus, and others ; while it is just the opposite 

 in the stems of SphagTitmi, where the epidermal layers are com- 

 posed of cells of a much larger and more delicate constitution 

 than the cells near the centre. 



There are many other points of similarity and contrast to be 



