Acacias which have phyllodias instead of leaves, some Myrtacesæ (Eucalyptus, Metrosideros, Melaleuca, and Leptospermum), and Casuarinas, give a uniform character to the vegetation of Australia and Tasmania (Van Diemen Island). Casuarinas with their leafless, thin, string-like, articulated branches, having the joints provided with membranous denticulated sheaths, have been compared by travellers, according to the particular species which fell under their observation, either to arborescent Equisetaceæ (Horsetails) or to our Scotch firs. (See Darwin, Journal of Researches, p. 449.) Near the coast of Peru the aspect of small thickets of Colletia and Ephedra also produced on my mind a singular impression of leaflessness. Casuarina quadrivalvis advances, according to Labillardière, to 48° S. lat. in Tasmania. The sad-looking Casuarina form is not unknown in India and on the east coast of Africa.
[23] p. 25.—“Needle-leaved trees.”
The family of Coniferæ holds so important a place by the number of individuals, by their geographical distribution, and by the vast tracts of country in the northern temperate zone covered with trees of the same species living in society, that we are almost surprised at the small number of species of which it consists,—even including members which belong to it in essential respects, but deviate from it in a degree by the shape of their leaves and their manner of growth (Dammara, Ephedra, and Gnetum, of Java and New Guinea). The number of known Coniferæ is not quite equal to three-fourths of the number of described species of palms; and there are more known Aroideæ than Coniferæ. Zuccarini, in his Beiträgen zur Morphologie der Coniferen (Abhandl. der mathem. physikal. Classe der Akademie der Wiss. zu München, Bd. iii. S. 752, 1837-1843), reckons 216 species, of which 165 belong to the northern and 51 to the southern hemisphere. Since my researches these proportionate numbers must be modified, as, including the species of Pinus, Cupressus, Ephedra, and Podocarpus, found by Bonpland and myself in the tropical parts of Peru, Quito, New Granada, and Mexico, the number of species between the tropics rises to 42. The most recent and excellent work of Endlicher, Synopsis Coniferarum, 1847, contains 312 species now living, and 178 fossil species found in the coal measures, the bunter-sandstone, the keuper, and the Jurassic formations. The vegetation of the ancient world offers to us more particularly forms which, by their simultaneous affinity with several different families of the present vegetable world, remind us that many intermediate links have perished. Coniferæ abounded in the ancient world: their remains, belonging to an early epoch, are found especially in association with Palms and Cycadeæ; but in the latest beds of lignite we also find pines and firs associated as now with Cupuliferæ, maples, and poplars. (Kosmos, Bd. i. S. 295-298, and 468-470; Engl. edit. p. 271-274, and lxxxix.)
If the earth’s surface did not rise to considerable elevations within the tropics, the highly characteristic form of needle-leaved trees would be almost unknown to the inhabitants of the equatorial zone. In common with Bonpland I have laboured much in the determination of the exact lower and upper limits of the region of Coniferæ and of oaks in the Mexican highlands. The heights at which both begin to grow (los Pinales y Encinales, Pineta et Querceta) are hailed with joy by those who come from the sea-coast, as indicating a climate where, so far as experience has hitherto shewn, the deadly malady of the black vomit (Vomito prieto, a form of yellow fever) does not reach. The lower limit of oaks, and more particularly of the Quercus xalapensis (one of the 22 Mexican species of oak first described by us), is on the road from Vera Cruz to the city of Mexico, a little below the Venta del Encero, 2860 (3048 E.) feet above the sea. On the western side of the highlands between the city of Mexico and the Pacific, the limit is rather lower down, for oaks begin to be found near a hut called Venta de la Moxonera, between Acapulco and Chilpanzingo, at an absolute elevation of 2328 (2480 E.) feet. I found a similar difference in the height of the lower limit of pine woods on the two-sides of the continent. On the Pacific side, in the Alto de los Caxones north of Quaxiniquilapa, we found this limit for Pinus Montezumæ (Lamb.), which we at first took for Pinus occidentalis (Swartz), at an elevation of 3480 (3709 E.) feet; while towards Vera Cruz, on the Cuesta del Soldado, pines are first met with at a height of 5610 (5950 E.) feet. Therefore both the kinds of trees spoken of above, oaks and pines, descend lower on the side of the Pacific than they do on the side of the Antillean sea. In ascending the Cofre di Perote, I found the upper limit of the oaks 9715 (10354 E.) feet, and that of the Pinus Montezumæ at 12138 (12936 E.) feet above the sea, or almost 2000 (2132 E.) feet higher than the summit of Etna. Considerable quantities of snow had fallen at this elevation in the month of February.
The more considerable the heights at which the Mexican Conifers are first met with, the more striking it appears to find in the Island of Cuba (where, indeed, on the borders of the torrid zone, northern breezes sometimes cool the atmosphere down to 6½° Reaumur, 46°.6 Fah.), another species of pine (P. occidentalis of Swartz), growing in the plains or on the low hills of the Isla de Pinos, intermixed with palms and mahogany trees (Swietenias). Columbus mentions a small pine wood (Pinal) in the journal of his first voyage (Diario del 25 de Nov. 1492), near Cayo de Moya, on the north-east of the Island of Cuba. In Hayti also, Pinus occidentalis descends from the mountains to the sea-shore, near Cape Samana. The trunks of these Pines, carried by the Gulf-stream to the Islands of Graciosa and Fayal in the Azores, were among the chief indications from which the great discoverer inferred the existence of unknown lands to the west. (See my Examen crit., T. ii. p. 246-259.) Is it true that in Jamaica, notwithstanding the height of its mountains, Pinus occidentalis is entirely wanting? We may also ask what is the species of Pinus found on the eastern coast of Guatimala, as P. tenuifolia (Benth.) probably belongs only to the mountains near Chinanta?
If we cast a general glance on the species which form the upper limits of arborescent vegetation in the northern hemisphere, from the frigid zone to the equator, we find, beginning with Lapland, that according to Wahlenberg, on the Sulitelma Mountain (lat. 68°) it is not needle-trees which form the upper limit, but that birches (Betula alba) extend much higher up than Pinus sylvestris;—whilst in the temperate zone, in the Alps (lat. 45¾°), Pinus picea (Du Roi) advances highest, leaving the birches behind; and in the Pyrenees (lat. 42½°), Pinus uncinata (Ram.) and P. sylvestris var. rubra: within the tropics, in lat. 19°-20° in Mexico, Pinus Montezumæ leaves far behind Alnus toluccensis, Quercus spicata, and Q. crassipes; while in the snow mountains of Quito at the equator, Escallonia myrtilloides, Aralia avicennifolia, and Drymis winteri, take the lead. The last-named tree, which is identical with Drymis granatensis (Mut.) and Wintera aromatica (Murray), presents, as Joseph Hooker has shewn (Flora Antarctica, p. 229), the striking example of the uninterrupted extension of the same species of tree from the most southern part of Tierra del Fuego and Hermit Island, where it was discovered by Drake’s Expedition in 1577, to the northern highlands of Mexico; or through a range of 86 degrees of latitude, or 5160 geographical miles. Where it is not birches (as in the far north), but needle trees (as in the Swiss Alps and the Pyrenees), which form the limit of arborescent vegetation on the highest mountains, we find above them, still nearer to the snowy summits which they gracefully enwreath with their bright garlands, in Europe and Western Asia, the Alp roses, the Rhododendra,—which are replaced on the Silla de Caracas and in the Peruvian Paramo de Saraguru by the purple flowers of another genus of Ericaceæ, the beautiful race of Befarias. In Lapland the needle-trees are immediately followed by Rhododendron laponicum; in the Swiss Alps by Rhododendron ferrugineum and R. hirsutum; in the Pyrenees by the R. ferrugineum only; and in the Caucasus by R. caucasicum. Decandolle found the Rhododendron ferrugineum growing singly in the Jura (in the Creux de Vent) at the moderate altitude of 3100 to 3500 (3304 to 3730 E.) feet, 5600 (5968 E.) feet lower down than its proper elevation. If we desire to trace the last zone of vegetation nearest to the snow line in the tropics, we must name, from our own observations, in the Mexican part of the tropical zone, Cnicus nivalis and Chelone gentianoides; in the cold mountain regions of New Granada, the woolly Espeletia grandiflora, E. corymbosa and E. argentea; and in the Andes of Quito, Culcitium rufescens, C. ledifolium, and C. nivale,—yellow flowering Compositæ which replace in the last-named mountains the somewhat more northerly Espeletias of New Granada, to which they bear a strong physiognomic resemblance. This replacement, the repetition of resembling or almost similar forms in countries separated either by seas or by extensive tracts of land, is a wonderful law of nature which appears to prevail even in regard to some of the rarest forms of vegetation. In Robert Brown’s family of the Rafflesieæ, separated from the Cytineæ, the two Hydnoras described by Thunberg and Drege in South Africa (H. africana and H. triceps) have their counterpart in South America in Hydnora americana (Hooker).
Far above the region of alpine plants, grasses, and lichens, and even above the limit of perpetual snow, the botanist sees with astonishment, both in the temperate and tropical zones, isolated phænogamous plants occur now and then sporadically on rocks which remain free from the general surrounding snowy covering, and which may possibly be warmed by heat ascending through open fissures. I have already spoken of the Saxifraga boussingaulti, which is found on the Chimborazo at an elevation of 14800 (15773 E.) feet; in the Swiss Alps, Silene acaulis has been seen at a height of 10680 (11380 E.) feet, being in the first-named case 600 (640 E.) feet, and in the second 2460 (2620 E.) feet above the limit of the snows, that limit being taken as it was in the two cases respectively at the time when the plants were found.
In our European Coniferæ, the Red and White Pine shew great and remarkable differences in respect to their distribution. While in the Swiss Alps the Red Pine (Pinus picea, Du Roi, foliis compresso—tetragonis; unfortunately called by Linnæus, and by most of the botanists of the present day, Pinus abies!) forms the upper limit of arborescent vegetation at a mean height of 5520 (5883 English) feet, only an occasional low growing mountain-alder (Alnus viridis, Dec., Betula viridis, Vill.) advancing now and then still nearer to the snow-line; the White Pine (Pinus abies, Du Roi, Pinus picea, Linn., foliis planis, pectinatodistichis, emarginatis) ceases, according to Wahlenberg, more than a thousand feet lower down. The Red Pine does not appear at all in the South of Europe, in Spain, the Appennines, and Greece; even on the northern slope of the Pyrenees it is seen only, as Ramond remarks, at great elevations, and is entirely wanting in the Caucasus. The Red Pine advances in Scandinavia farther to the north than the White Pine, of which last-named tree there is in Greece (on Mounts Parnassus, Taygetus, and Œta) a long needled variety (foliis apice integris, breviter mucronatis), the Abies Apollinis of Link. (Linnæa, Bd. xv. 1841, S. 529; and Endlicher, Synopsis Coniferarum, p. 96.)
On the Himalaya the Coniferæ are distinguished by the great thickness and height of their trunks, and by the length of their leaves. The Deodwara Cedar, Pinus deodara (Roxb.),—(properly, in Sanscrit, dêwa-dâru, timber of the Gods),—which is from 12 to 13½ feet thick, is the great ornament of the mountains. It grows in Nepaul to 11000 (11720 E.) feet above the level of the sea. More than 2000 years ago the Deodara supplied the materials for the fleet of Nearchus on the Hydaspes (the present Behut). In the valley of Dudegaon, north of the copper mines of Dhunpour in Nepaul, Dr. Hoffmeister, so early lost to science, found the Pinus longifolia of Royle (the Tschelu Pine) growing among tall stems of the Chamærops martiana of Wallich. (Hoffmeister’s Briefe aus Indien während der Expedition des Prinzen Waldemar von Preussen, 1847, S. 351.) Such an intermixture of pineta and palmata had excited the surprise of the companions of Columbus in the New Continent, as a friend and cotemporary of the Admiral, Petrus Martyr Anghiera, has informed us. (Dec. iii. lib. 10, p. 68.) I saw myself this intermixture of pines and palms for the first time on the road from Acapulco to Chilpanzingo. The Himalaya, like the Mexican highlands, has, besides Pines and Cedars, also the forms of Cypresses (Cupressus torulosa, Don), of Yews (Taxus wallichiana, Zuccar.), of Podocarpus (P. nereifolia, Robert Brown), and of Juniper (Juniperus squamata, Don., and J. excelsa, Bieberst; Juniperus excelsa is also found at Schipke in Thibet, in Asia Minor, in Syria, and in the Greek Islands). Thuja, Taxodium, Larix, and Araucaria, are forms found in the New Continent, but wanting in the Himalaya.
Besides the 20 species of Pines which we already know from Mexico, the United States of North America, which in their present extent reach to the Shores of the Pacific, have 45 described species, while Europe has only 15. There is a similar difference in respect to Oaks: i. e. greater variety of forms in the New Continent which extends continuously through a greater extent of latitude. The recent very exact researches of Siebold and Zuccarini have, however, completely refuted the previous belief, that many European species of Pines extend also across the whole of Northern Asia to the Islands of Japan, and even grow there, interspersed, as Thunberg has stated, with genuine Mexican species, the Weymouth Pine, Pinus Strobus of Linnæus. What Thunberg took for European Pines are wholly different and distinct species. Thunberg’s Red Pine (Pinus abies, Linn.) is P. polita, (Sieb.) and is often planted near Buddhistic temples; his common Scotch Fir (Pinus sylvestris) is P. Massoniana (Lamb.); his P. cembra (the German and Siberian pine with eatable seeds) is P. parviflora (Sieb.); his common Larch (P. larix) is P. leptolepis (Sieb.); and his supposed Taxus baccata, the fruits of which are eaten by Japanese courtiers in case of long-protracted court ceremonials, (Thunberg, Flora Japonica, p. 275), constitutes a distinct genus, and is the Cephalotaxus drupacea of Siebold. The Islands of Japan, notwithstanding the vicinity of the Continent of Asia, have a very distinct character of vegetation. Thunberg’s supposed Japanese Weymouth Pine, (Pinus Strobus) which would offer an important phenomenon, is only a planted tree, and is besides quite distinct from the American species of Pine. It is Pinus korajensis (Sieb.), and has been brought to Nipon from the peninsula of Corea, and from Kamtschatka.