774 



ZONES AND REGIONS [Pt. Ill, Sect. IV 



it alone prevails where the soil permits. Climatic conditions are the most 

 favourable conceivable for grassland. During the whole summer light 

 showers fall daily, which, wetting the superficial layer of soil, quickly 

 compensate the shallow-rooted grasses for the great loss of water by 

 transpiration during the sunny hours. Only stony permeable places are 

 abandoned to deep-rooted shrubs and perennial herbs. Even winter is 

 favourable to the grass, if only indirectly so, as it is poor in atmospheric 

 precipitations and has many sunny days. But we know that bright 

 winters, owing to their desiccating effects, are hostile to trees. This is, 

 however, much more marked at alpine altitudes, where strong insolation 

 favours the transpiration of branches, than in the lowlands. Frequency 



Fig. 472. 1. Rhododendron ferrugineum. 2. R. hirsutum. Two-thirds natural size. 



of summer showers and a lower altitude cause the grassland of the Swiss 

 Alps to possess a much less xerophilous stamp than in mountains of warmer 

 ranges and to be classed with the meadow-type rather than with the 

 steppe-type. The carpet of vegetation is not discontinuous, and only in 

 dry places does it include stiff grasses with narrow involute leaves, like 

 Nardus stricta, Festuca ovina, var. alpina, and associated with them, very 

 hairy perennial herbs, such as Leontopodium alpinum, Potentilla nivea, 

 Senecio incanus, and others. Wherever the water remains longer, the 

 structure of most of the plants is less xerophilous. Marked protective 

 contrivances against drought are exhibited by plants on rocks covered by 

 a thin layer of earth, or in crevices in rocks, where the water rapidly 

 evaporates or flows away. In such places many of the best known and 

 most characteristic alpine plants show themselves, for instance, Dryas octo- 

 petala, Globularia cordifolia, the alpine Crassulaceae (species of Sedum and 



