MOSSES AND LIVERWORTS. 263 



and of Andraea, are especially interesting in this 

 respect. 



Those of Polytrichum have been very well described 

 by Kerner in his Natural History of Plants. The 

 figures show clearly how the escape of moisture is 

 prevented, as far as possible, in dry weather; and how 

 the green cells of the upright plates which run longi- 

 tudinally down the leaf, stand out in moist weather to 

 get the greatest possible amount of light. 



Rhacomitrium leaves generally end in long fine 

 points. In the dry state all the leaves contract upon 

 the stem, and the plant seems entirely covered by 

 woolly hairs, which are the leaf-tips. They look very 

 like the woolly hairs characteristic of desert plants, and 

 they fulfil the same purpose, that of keeping in moisture, 

 and, probably, also of keeping out cold. 



Fontinalis antipyretica is altogether different from 

 these wall mosses. It grows in rapid streams, especi- 

 ally in mountain streams, and is often found in great 

 numbers and mixed with liverworts and other mosses. 

 The leaves are arranged in distinct rows, and in such a 

 way that they shelter one another from the current. 

 The hairs, by means of which it holds to the stones, are 

 also well worth examination. 



Climacium, a "wood-floor " moss, looks like a miniature 

 tree with an erect stem and several branches. 



To all British and Irish students peat-moss is certainly 

 of great importance. In Ireland bogs occupy some- 

 thing like one-seventh part of the surface. In Scotland 

 there are many square miles of moss which are still 

 entirely uncultivated, and yield a very scanty pasturage 

 to sheep, or to wild animals. We may suppose the 

 formation of a peat moss to have been as follows, 

 though it must not be considered that any peat moss 



