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.
[20] p. 4.—“The Cactus form.”
If we take the natural family of the Opuntiaceæ separated from the Grossulariaceæ (the species of Ribes), and, viewed as it is by Kunth (Handbuch der Botanik, S. 609), we may well regard it as belonging exclusively to America. I am aware that Roxburgh, in the Flora Indica (inedita), cites two species of Cactus as belonging to South Eastern Asia;—Cactus indicus and C. chinensis. Both are widely disseminated, and are found in a wild state (whether they were originally wild or have become so), and are distinct from Cactus opuntia and C. coccinellifer; but it is remarkable that the Indian plant (Cactus indicus) has no ancient Sanscrit name. Cactus chinensis has been introduced in St. Helena as a cultivated plant. Now that a more general interest has at length been awakened on the subject of the original distribution of plants, future investigation will dispel the doubts which have been felt in several quarters respecting the existence of true Asiatic Opuntiaceæ. In the animal kingdom particular forms are found to occur singly. Tapirs were long regarded as a form exclusively characteristic of the New Continent; and yet the American tapir has been found as it were repeated in that of Malacca (Tapirus indicus, Cuv.)
Although the species of Cactus belong, generally speaking, more properly to the tropical regions, yet some are indigenous in the temperate zone, as on the Missouri and in Louisiana, Cactus missuriensis and C. vivipara; and Back saw with astonishment the shores of Rainy Lake, in north lat. 48° 40´, covered with C. opuntia. South of the equator the species of Cactus do not extend beyond the Rio Itata, in lat. 36°, and the Rio Biobio, in lat. 37° 15´. In the part of the Andes which is situated between the tropics, I have seen species of Cactus (C. sepium, C. chlorocarpus, C. bonplandii) growing on elevated plains nine or ten thousand (French) feet (about 9590 and 10660 English) above the level of the sea; but a still more alpine character is shewn in latitudes belonging to the temperate zone, in Chili, by the Opuntia ovallei, which has yellow flowers and a creeping stem. The upper and lower limits beyond which this plant does not extend have been accurately determined by barometric measurement by the learned botanist Claude Gay: it has never been found lower than 6330 French (6746 English) feet, and it reaches and even passes the limits of perpetual snow, having been found on uncovered masses of rock rising from amongst the snows. The last small plants were collected on spots situated 12820 French (13663 English) feet above the level of the sea. (Claudio Gay, Flora Chilensis, 1848, p. 30.) Some species of Echino-cactus are also true alpine plants in Chili. A counterpart to the fine-haired Cactus senilis is found in the thick-wooled Cereus lanatus, called by the natives Piscol, which has handsome red fruit. We found it in Peru, near Guancabamba, when on our journey to the Amazons river. The dimensions of the different kinds of Cactaceæ (a group on which the Prince of Salm-Dyck has been the first to throw great light) offer great variety and contrasts. Echinocactus wislizeni, which is 4 feet high and 7 feet in circumference (4 feet 3 inches and 7 feet 5 inches English), is still only the third in size, being surpassed by E. ingens (Zucc.) and by E. platyceras (Lem.) (Wislizenus, Tour to Northern Mexico, 1848, p. 97.) The Echinocactus stainesii reaches from 2 to 2½ feet diameter; E. visnago, from Mexico, upwards of 4 English feet high, is above 3 English feet diameter, and weighs from 700 to 2000 lbs.: while Cactus nanus, which we found near Sondorillo, in the province of Jaen, is so small that, being only slightly rooted in the sand, it gets between the toes of dogs. The Melocactuses, which are full of juice in the dryest seasons like the Ravenala of Madagascar (forest-leaf in the language of the country, from rave, raven, a leaf, and ala, the Javanese halas, a forest), are vegetable fountains; and the manner in which the horses and mules stamp them open with their hoofs, at the risk of injury from the spines, has been already mentioned (Vol. I p. 19). Since the last quarter of a century Cactus opuntia has extended itself in a remarkable manner into Northern Africa, Syria, Greece, and the whole of the South of Europe; even penetrating, in Africa, from the coasts far into the interior of the country, and associating itself with the indigenous plants.
When one has been accustomed to see Cactuses only in our hothouses, one is astonished at the degree of density and hardness which the ligneous fibres attain in old cactus stems. The Indians know that cactus wood is incorruptible, and excellent for oars and for the thresholds of doors. There is hardly anything in vegetable physiognomy which makes so singular and ineffaceable an impression on a newly arrived person, as the sight of an arid plain thickly covered, like those near Cumana, New Barcelona, and Coro, and in the province of Jaen de Bracamoros, with columnar and candelabra-like divided cactus stems.
[21] p. 24.—“Orchideæ.”
The almost animal shape of blossoms of Orchideæ is particularly striking in the celebrated Torito of South America (our Anguloa grandiflora); in the Mosquito (our Restrepia antennifera); in the Flor del Espiritu Santo (also an Anguloa, according to Floræ Peruvianæ Prodrom. p. 118, tab. 26); in the ant-like flower of the Chiloglottis cornuta (Hooker, Flora antarctica, p. 69); in the Mexican Bletia speciosa; and in the highly curious host of our European species of Ophrys: O. muscifera, O. apifera, O. aranifera, O. arachnites, &c. A predilection for this superbly flowering group of plants has so increased, that the number cultivated in Europe by the brothers Loddiges in 1848 has been estimated at 2360 species; while in 1843 it was rather more than 1650, and in 1813 only 115. What a rich mine of still unknown superb flowering Orchideæ the interior of Africa must contain, if it is well watered! Lindley, in his fine work entitled “The Genera and Species of Orchideous Plants,” described in 1840 precisely 1980 species; at the end of the year 1848 Klotzsch reckoned 3545 species.
While in the temperate and cold zones there are only “terrestrial” Orchideæ, i. e. growing on and close to the ground, tropical countries possess both forms, i. e. the “terrestrial” and the “parasitic,” which grow on trunks of trees. To the first-named of these two divisions belong the tropical genera Neottia, Cranichis, and most of the Habenarias. We have also found both forms growing as alpine plants on the slopes of the chain of the Andes of New Granada and Quito: of the parasitical Orchideæ (Epidendreæ), Masdevallia uniflora (at 9600 French, or about 10230 English feet); Cyrtochilum flexuosum (at 9480 French, or about 10100 English feet); and Dendrobium aggregatum (8900 French, or about 9480 English feet): and of the terrestrial Orchideæ, the Altensteinia paleacea, near Lloa Chiquito, at the foot of the Volcano of Pichincha. Claude Gay thinks that the Orchideæ said to have been seen growing on trees in the Island of Juan Fernandez, and even in Chiloe, were probably in reality only parasitical Pourretias, which extend at least as far south as 40° S. lat. In New Zealand we find that the tropical form of Orchideæ hanging from trees extends even to 45° S. lat. The Orchideæ of Auckland’s and Campbell’s Islands, however (Chiloglottis, Thelymitra, and Acianthus), grow on the ground in moss. In the animal kingdom, one tropical form at least advances much farther to the south. In Macquarie Island, in lat. 54° 39´, nearer to the South Pole therefore than Dantsic is to the North Pole, there is a native parrot. (See also the section Orchideæ in my work de Distrib. geogr. Plant., pp. 241-247.)
[22] p. 25.—“The Casuarinæ.”