Mosses and Peat 



that its cushions are very close and crowded and soon 

 tend to swell up into small dome-shaped or convex 

 projections. Both leaf and stem are full of empty cells 

 which act as water cisterns and possess fine spiral 

 strengthening fibres to prevent collapse. The appear- 

 ance of these cells reminds one of indiarubber tubing, 

 strengthened by a spiral wire inside. 



Suppose now that a wet marsh is beginning to be 

 dotted about by separate Sphagnum plants. Each is 

 a circular cushion convex upwards and always widen- 

 ing at the circumference. Every shower of rain saturates 

 them ; any surplus water simply collects under the 

 cushions. In time the cushions begin to touch one 

 another, but there will be some inequality of growth 

 so that the surface is uneven with holes full of water 

 between the bulging convex surfaces. The moss, how- 

 ever, still goes on growing upwards, and eventually 

 forms a huge accumulation of peat, which may occupy 

 the whole marsh. In the middle it will be on the 

 whole higher, and it will slope as a very gently arched 

 dome from the centre to every part of the circumfer- 

 ence. This mass of peat is composed of the dead re- 

 mains of the Sphagnum itself, and of all other plants 

 which succeed in growing there ; they do not decay, 

 because the living crust of Sphagnum being saturated 

 with water and very closely packed together, does not 

 permit the free passage of oxygen to the dead vegetable 

 matter below. Moreover, there are but few bacteria, for 

 there are antiseptic substances in peat. Hence such 

 peat mosses are extremely valuable from a historical 

 point of view. One can not only distinguish the 

 changes in vegetation that have occurred since the 

 peat moss began to grow, but if there be bones of 

 animals or prehistoric canoes and other implements, 

 they are quite well preserved (see Chap. XX,). 



73 



