ILLUSTRATIONS (19). HEATHS. 309 



and Calluna vulgaris, cover large tracts of country, extending 

 from the plains of Germany, and from France and England, to 

 the extremity of Norway ; Southern Africa presents the most 

 varied assortment of species. One single species, Erica um- 

 bellata, which is indigenous in the southern hemisphere, at 

 the Cape of Good Hope, is again found in Northern Africa, 

 Spain, and Portugal. Erica vagans and E. arborea also 

 belong to the opposite coasts of the Mediterranean. The 

 former is met with in Northern Africa, in the neighbour- 

 hood of Marseilles, in Sicily and Dalmatia, and even in Eng- 

 land; the second in Spain, Istria, Italy, and the Canaries."* 

 The common heath, Calluna vulgaris (Salisbury), which is 

 a social plant, covers large tracts from the mouth of the 

 Scheldt to the western declivity of the Ural. Beyond the 

 Ural both Oaks and Heaths disappear. Both are wanting 

 in the whole of Northern Asia, and in all Siberia, as 

 far as the Pacific. Gmelinf and Pallas J have expressed 

 their astonishment at this disappearance of Calluna vulgaris ; 

 which, on the eastern declivity of the Ural chain is even 

 more decided and more sudden than one might be led to 

 conclude, from the words of the last-named great naturalist. 

 Pallas merely says, "ultra Uralense jugum sensim deficit, 

 vix in Isetensibus campis rarissime apparet, et ulteriori 

 Sibirise plane deest." Chamisso, Adolph Erman, and Heinrich 

 Kittlitz collected Andromedas but no Calluna in Kamtschatka 

 and on the north-west coast of America. The accurate 

 knowledge which Ave at present possess of the mean tem- 

 perature of different portions of Northern Asia, as well as 

 of the distribution of annual heat throughout the different 

 seasons, in no w T ay explains the non-advance of the Heath to 

 the east of the Ural. Dr. Joseph Hooker has treated with 

 much ingenuity, in a note to his " Flora Antarctica," of 

 the two contrasting phenomena of the distribution of plants, 

 " uniformity of surface accompanied by a similarity of vege- 

 tation ", and again, "instances of a sudden change in the 

 vegetation, unaccompanied with any diversity of geological 



* Klotsch, Ueber die geographische Verbreitung der Erica- Arten 

 mil bleibender Blumenhrone. Manuscr. 

 f Flora Sibirica, t. iv., p. 129. 

 % Flora Bossica, t. i., pars 2, p. 53. 



