50 



BRITISH MOSSES. 



have produced considerable physical 

 effects. 



(1) Everyone knows the different 

 effects of rain falling on a land of 

 bare rock or sand, like the Sinaitic 

 desert, and on a porous soil. In the 

 one case it produces a freshet or a 

 flood, that leaves no water behind ; 

 in the other it is held for a while in 

 suspense, and only gradually passes 

 into the streams. The glaciers and 

 the Sphagnum beds of the mountains 

 of Europe alike act as compensation 

 reservoirs receive large quantities 

 of moisture as it falls, and retain it 

 till the drier season comes, when 

 part of it gradually passes away ; but 

 for these reservoirs, many of the rivers 

 would exhibit a far greater shrinkage 

 in summer and autumn than is now 

 the case. But (2) the Sphagnum beds have become peat, 

 and have gradually filled up the ancient lakes and morasses, 

 and turned water into dry land. It is true that peat appears 

 under some circumstances to be formed by other vegetables 

 than Sphagnum, and in all cases it has probably some 

 other plants or roots growing amongst it. Mr. Darwin 

 tells us that in Terra del Fuego and the Chonos Archipelago, 

 peat is formed by two phanerogamous plants, of which 

 one at least seems endowed with an immortality something 

 like that of the Sphagnum ; and the peat of the fens of 



Fia. 31. Stem of 

 Sphagnum mollus- 

 cum, magnified, show- 

 ing MM, the utricles or 

 flask-shaped cells. 

 After Schimper. 



