68 COMPOUND ORGANS OP PLANTS. 



facing the north, and are most abundant in the temperate 

 regions of the earth. In tropical climates, they are found 

 chiefly on the summit of mountains, where the heat and dry- 

 ness of the climate are moderated by the elevation of the 

 land. In summer, they are seldom seen, except in moist, 

 shady spots, such as grow in tufts on the tops of walls, or the 

 surface of exposed rooks, being burnt up, or as it were dried 

 to dust, so that they escape our notice. Yet even at this 

 season, a shower of rain will revive them and cause them to 

 burst forth into verdure. But their beauty is evanescent; 

 and they soon wither and disappear from the wall or rook on 

 which they were seen. In autumn, as the temperature de- 

 clines, the mosses make their appearance, and in winter 

 they are found in perfection, beautifying this desolate season 

 of the year. 



86. The mosses are plants having a distinct stem or axis 

 of growth, around which their minute leaves are arranged with 

 the greatest regularity and beauty. These leaves, and, in 

 fact, the whole plant, assume a regular specific form, being, 

 as to their margin, entire, serrate, or denticulate, with con- 

 densed cells in their centre, which form a sort of midrib or 

 nerve. Occasionally, however, the leaves are nerveless, as 

 in Hypnum purum, a British species. 



87- Sometimes the stem is procumbent, or creeps along the 

 ground ; the branches fork and spread, emitting rootlets from 

 every part of their under surface, which doubtless perform 

 their part in absorption ; and the capsules or fruit come out 

 laterally, or from the side of the branches. In other species, 

 the stem takes an ascending direction, the rootlets are con- 



