Chap. IV] MOUNTAIN REGIONS IN TEMPERATE ZONES 775 



Sempervivum, Rhodiola rosea). Saxifraga Aizoon, Draba aizoides, also species 



of Primula (Fig. 475) and Androsace (Fig. 473). Only in such places on 



the Simplon, though there in great abundance, does the rare Senecio 



uniflorus grow, whereas S. incanus inhabits the 



neighbouring dry grassland, and the hybrid 



occupies the intermediate spaces. Most of these 



plants have the rosette-form or cushion-form. 



Round these blocks of rock water penetrates 



deeply into the soil, which is consequently 



preferred as a habitat by alpine shrubs, such 



as Juniperus nana, Azalea procumbens, Arcto- 



staphylos alpina, and others that spread over 



the surface of the rocks. 



Screes occupy large areas in high parts on 

 the Alps, as in other mountains, without how- 

 ever being so extensive as on desert-mountains, 

 or in New Zealand. These screes are frequently covered by dwarf-shrub ; 

 if however of recent origin, they exhibit a peculiar vegetation of deep-rooted 



Fig. 473. Androsace helvetica. 

 Natural size. 



Fig. 474. Salix reticulata, a creeping shrub of the alpine meadow. Natural size. 



perennial herbs, which for the most part are confined to these habitats, such as 

 Linaria alpina, Oxyria digyna,Thlaspi rotundifolium, and others. Calcareous 

 scree supports Papaver alpinum, one of the greatest ornaments of the Alps, 

 also Viola cenisia and others. Fleshy, glaucous, glabrous, or at most 



