Note 19 — PHYSIOGNOMY OF PLANTS.

p. 23—“Heaths.”

In these physiognomic considerations we by no means comprise under the name of Heaths the whole of the natural family of Ericaceæ, which on account of the similarity and analogy of the floral parts includes Rhododendron, Befaria, Gaultheria, Escallonia, &c. We confine ourselves to the highly accordant and characteristic form of the species of Erica, including Calluna (Erica) Vulgaris, L., the common heather.

While, in Europe, Erica carnea, E. tetralix, E. cinerea, and Calluna vulgaris, cover large tracts of ground from the plains of Germany, France, and England to the extremity of Norway, South Africa offers the most varied assemblage of species. Only one species which is indigenous in the southern hemisphere at the Cape of Good Hope, Erica umbellata, is found in the northern hemisphere, i. e. in the North of Africa, in Spain, and Portugal. Erica vagans and E. arborea also belong to the two opposite coasts of the Mediterranean: the first is found in North Africa, near Marseilles, in Sicily, Dalmatia, and even in England; the second in Spain, Italy, Istria, and in the Canaries. (Klotsch on the Geographical Distribution of species of Erica with persistent corollas, MSS.) The common heather, Calluna vulgaris, is a social plant covering large tracts from the mouth of the Scheldt to the western declivity of the Ural. Beyond the Ural, oaks and heaths cease together: both are entirely wanting in the whole of Northern Asia, and throughout Siberia to the shores of the Pacific Ocean. Gmelin (Flora Sibirica, T. iv. p. 129) and Pallas (Flora Rossica, T. i. Pars 2, p. 58) have expressed their astonishment at this disappearance of the Calluna vulgaris,—a disappearance which, on the eastern declivity of the Ural Mountains, is even more sudden and decided than might be inferred from the expressions of the last-named great naturalist. Pallas says merely: “ultra Uralense jugum sensim deficit, vix in Isetensibus campis rarissime apparet, et ulteriori Sibiriæ plane deest.” Chamisso, Adolph Erman, and Heinrich Kittlitz, have found Andromedas indeed in Kamtschatka, and on the North West coast of America, but no Calluna. The accurate knowledge which we now possess of the mean temperature of several parts of Northern Asia, as well as of the distribution of the annual temperature into the different seasons of the year, affords no sort of explanation of the cessation of heather to the east of the Ural Mountains. Joseph Hooker, in a note to his Flora Antarctica, has treated and contrasted with great sagacity and clearness two very different phenomena which the distribution of plants presents to us: on the one hand, “uniformity of surface accompanied by a similarity of vegetation;” and on the other hand, “instances of a sudden change in the vegetation unaccompanied by any diversity of geological or other features.” (Joseph Hooker, Botany of the Antarctic Voyage of the Erebus and Terror, 1844, p. 210.) Is there any species of Erica in Central Asia? The plant spoken of by Saunders in Turner’s Travels to Thibet (Phil. Trans. Vol. lxxix. p. 86), as having been found in the Highlands of Nepaul (together with other European plants, Vaccinium myrtillus and V. oxycoccus) and described by him as Erica vulgaris, is believed by Robert Brown to have been an Andromeda, probably Andromeda fastigiata of Wallich. No less striking is the absence of Calluna vulgaris, and of all the species of Erica throughout all parts of the Continent of America, while the Calluna is found in the Azores and in Iceland. It has not hitherto been seen in Greenland, but was discovered a few years ago in Newfoundland. The natural family of the Ericaceæ is also almost entirely wanting in Australia, where it is replaced by Epacrideæ. Linnæus described only 102 species of the genus Erica; according to Klotzsch’s examination, this genus really contains, after a careful exclusion of all mere varieties, 440 true species.