ALI'IXK FLORA. 209 



through the air*. Besides, there is a relation between the dis- 

 tribution of these Alpine plants and the dispersion of the Alpine 

 erratic rocks. On the Uetliberg the Alpine toad-flax (Linaria 

 afyina) and the willow herb (Epilobium Fleischeri) are found 

 associated exactly as on the terminal moraines and in the loca- 

 lities deserted by Alpine glaciers. These arctic plants occur on 

 the Albis, the Bachtel, and the Lagern, at the same elevation 

 with rock-masses coming from high mountains. In this respect 

 the localization of the two Swiss Alpine roses (Rhododendron) is 

 very instructive. The species with fringed leaves (R. hirsutum, 

 Linn.) keeps chiefly to the limestone mountains, and occupies 

 a lower zone than the rusty-leaved species (R. ferrugineum, 

 Linn.). We should therefore expect to find the former and not 

 the latter in the Juraf. Yet it is only the rusty-leaved Alpine 

 rose that occurs in the Jura, and this is precisely the species 

 that grows everywhere in the mountains between the Simplon 

 and St. Bernard (which, as has been already seen, furnished the 

 erratic blocks on the Jura), whilst the fringe-leaved species is 

 wanting there J. As the rusty-leaved Alpine rose has the same 



* On the erratic blocks of the plain a good many Alpine Cryptogamia are 

 found, and especially Lichens (for instance, according to Dr. Hepp, Lecidia 

 badio-atrdj spuria, discolor, micropsis, dispora, atro-alba, saxatilisj and Lecanora 

 badia). It may be remarked that on the plough-stone (Pflugstein) of Erlen- 

 bach an Alpine and northern fern (Asplenium septentrionale] is found which 

 occurs nowhere else in the whole Canton of Zurich. 



t In the Bernese Alps opposite the Jura (the Stockhorn chain) Rhodo- 

 dendron hirsninm is abundant. 



\ The fringe-leaved Alpine rose occurs in the mountains of Savoy, for ex- 

 ample at the Mole, and the Brezon, near Bonneville ; but as it is wanting in 

 the intermediate localities (between Bonneville and the Jura), for instance at 

 the Saleve, it is probable that it reached the Jura with the erratics of the 

 glaciers coming from the Alps. Of the 198 species of Alpine plants diffused 

 over the Jura, 179 also occur in the Alps of the Canton of Valais, so that the 

 great majority of these plants might come from that Canton. It is, however, 

 very probable that the Alpine plants have reached the Jura by another course, 

 since a certain number of Arcto-Alpine plants are found in the Jura. There 

 has also evidently been an immigration coming from the south-west, by 

 which the flora of the Jura has been enriched with Mediterranean elements. 

 But as the Jura sinks to the south of the Cluses de Nantua, and nearly all 

 the Alpine plants there disappear to flourish again near the Grande-Char- 

 treuse, where the mountains rise again to the Alpine region, we must not 

 seek in that district for the origin of the Alpine flora of the Jura. In this 



VOL. II. F 



