ADAPTATION TO CLIMATE. 341 



from the cold in such regions is their low stature. Many of the 

 herbaceous plants have very short stems, and the leaves lie close 

 to the soil, the plants and flowers sometimes half covered with 

 the snow. The heat absorbed by the soil is thus imparted to 

 the plant. Trees in such regions (if the elevation or latitude 

 is not beyond the tree line) have very short and crooked stems, 

 and sometimes are of great age when only a foot or more high, 

 and the trunk is quite small. In figure 276 are shown some 

 birch trees from Greenland, one third natural size, the entire 

 tree being here shown. Similarly figure 277 represents some 

 of the arctic willows, one third natural size. 



509. Some plants of swamps and moors present characters 

 of arctic or desert vegetation. — Many of the plants of our 

 swamps and moors have the characters of arctic or of desert 

 vegetation, i.e., small, thick leaves, or leaves with a stout 

 epidermis. The labrador tea (Ledum latifolium), an inhabitant 

 of cold moors or mountain woods, has thick, stout leaves with 

 a hard epidermis on the upper side, and the lower side of the 

 leaves is densely covered with brown, woolly hairs. Transpira- 

 tion is thus lessened. This is necessitated because of the cold 

 soil and water of the moor surrounding the roots, which under 

 these conditions absorb water slowly. Were the leaves broad 

 with a thin and unprotected epidermis, transpiration would be 

 in excess of absorption, and the leaves would wither. Cassan- 

 dra, or leather-leaf, and chiogenes, or creeping snowberry, are 

 other examples of these shrubs growing in cold moors. 



510. Hairs on young leaves protect against cold and wet. 

 —Hairs on young leaves in winter buds afford protection from 

 cold and from the wet. The young leaves of the winter buds 

 of many of our ferns are covered with a dense felt of woolly 

 hairs. In species of osmunda this is very striking. The leaves 

 ire quite well formed, though small, during the autumn, and 

 the sporangia are nearly mature. The hairs are so numerous, 

 and so closely matted together, that they can be torn off in the 

 form of a thick woolly cap. 



