INFLUENCK OF UKAT ON CONFIGURATION .\M> DISTRIBUTION OK PLANTS. 523 



suiiiiiier, as, for oxninple, Lamium album, produce late in the autumn, under a 

 very low tempemture (if they bloom a second time), corollas whose upper side is 

 tin;,'ed with red; and that in the winter, and in frosty hahitiits, the ray-florets 

 also of many Coniposit;e, as, for example, of the well-known Daisj^ (Bdlis perennia), 

 are coloured red ou that side which is turned towards the sky when the ca]'ituluiii 

 is closed, and towards the gx-ound when the capitulum is open. 



INFLUENCE OF UEAT ON TUE CONFlLiUKATiON AND DISTRIBUTION 



OF PLANTS. 



On high mountains near the snow-line, and generally in all those disti-icts 

 where the heat supplied to the plants is extremely scant, there occurs, together 

 with a production of anthocyanin, a dwarf and tufted habit. Usually this 

 phenomenon is explained by the large amount of snow, which must have a great 

 efl'oct in these frosty heights during the long winter, and it is believed that high 

 Alpine plants are protected by this form and position of their stems and leaves from 

 injury by the pressure of snow. It cannot indeed be denied that the pressure of 

 the snow has some influence on the form and direction of the stem-structures, and 

 this influence will be explained fully in the following pages in a particularly 

 instructive example, viz. in the mountain pines. But this nestling on the gi-ouiid 

 of plants growing in the high Alps can onh^ be partially referred to this cause. 



It is a mistake to suppose that the annual snow-fall increases with the height. 

 The amount of snow which falls attains a maximum at about 2500 metres above 

 the sea-level. This height marks only the upper limit of mountain pines, dwarf 

 junipers, alders, and rhododendrons. Above this the fall diminishes, and at a height 

 of 3000 metres the snow is no deeper than far down in the valleys. Even where 

 the maximum fall occurs trees are still met with; there are yet larches and Arolla 

 pines, which, on account of the gi-eat elasticity of their branches and the downward 

 direction of their older boughs, can bear very heavy weights of snow without 

 becoming broken or crushed. The willows of mountain regions, chai-acterized by 

 the way in which their elongated stems and branches are pressed to the earth 

 {Salix serpyllifolia, S. retusa, Jacquiniana, reticulata), and which are represented 

 in fig. 131, grow, howevei-, far above the tree limit, at a height above the sea 

 where the depth of snow, already beginning to diminish, is in no case greater than 

 ill tlio valli-ys, where Purple and Sweet Willows, and other species of large-leaved 

 willows raise their straight stems several metres high above the ground on the 

 banks of streams. It must also be remembered that the woody growths close to 

 the ground in high Alpine regions are very often established on steep places, whore 

 the snow could not easily lie, could in no instance be deeply piled up, and could not 

 exert a pressure on the stems and branches. The delicate Thyme-leaved Willow 

 (Salix aerpyllifolia) nestles with an especial predilection to the surfaces of rocks, 

 and covers them with an actual carpet, and the Buckthorn (Rhamnus piimila) is 

 found exclusively on steep declivities, where it roots in the crevices of the narrow 



