©riginal J^rticlcs. 



ox MOSSES .''—i Concluded.) 

 By Wm. West. 



TdrapJiis is the link that binds the last to those having a peristome, 

 and here the firm epidermis of the upper part of the theca falls off as 

 a lid, the whole internal tissue of the latter splitting across into four 

 valves, the origin and structure of which are very different from a peris- 

 tome ; for, except in Polytrichace<2, neither the teeth nor the cilia consist 

 of cellular tissue, but of thickened and hardened parts ol the walls of a 

 layer of cells, which is separated by layers of thin-walled cells from 

 the epidermis which forms the lid. These latter layers, as well as the 

 delicate parts of the former, disappear, while the thickened parts of 

 the wall remain after the lid is cast off. When the peristome is 

 double, the outer row is said to be composed of teeth, the inner of 

 cilia. There is a row of epidermal cells, thickened on the outside ; 

 these cells are modified in shape where the annulus is formed, several 

 layers of cells come next, and inside these is the layer of cells situated 

 over the air-cavity from which the peristome is formed. Near the 

 base of this layer are some thickened cells, which serve to unite the 

 edge of the theca with the base of the teeth. The outer face of the 

 layer of cells from which the peristome is formed, is thickened, and 

 it forms the teeth ; the cilia are formed from the thickened axiul face 

 of the same layer ot cells ; where and when this inner face does not 

 thicken, there are no cilia formed. The most highly developed 

 mosses belong to Pohjtrkhim^ whose theca differs in structure from 

 the other genera. The teeth of the peristome are composed of 

 bundles of thickened prosenchymatous cells, having the shape of a 

 horse-shoe, the branches of two adjoining bundles form together one 

 of the teeth. There is also a layer of cells uniting the points of the 

 teeth after the lid is cast off. The spore-sac in some species (as in 

 Polytrichum piliferum) is separated by an air cavity from the columella, 

 which is penetrated like the outer air cavity, by conferva-like rows of 

 cells. The seta is swollen at its junction with the theca, in some 

 species, forming an apophysis. 



Mosses are subject to varieties as well as phasnogamous plants, 

 and some varieties of one species sometimes differ from each other 

 more than neighbouring species which are admitted as distinct. 

 Hijpnum cupressiforme is an example. The peristome is sometimes 

 present and sometimes absent in some species, as in Enccqdypta vuU 

 garis^ hence the distinction of species is sometimes difficult. 

 N. S., Vol. iv., Sept., 1878. 



