[91]. p. 226—“Orchideæ.”
The almost animal-like form occasionally observed in blossoms of the Orchideæ is most strongly marked in Anguloa grandiflora, celebrated in South America as the Torito; in the Mosquito (our Restrepia antennifera); in the Flor del Espiritu Santo (likewise an Anguloa, according to Floræ Peruvianæ Prodrom. p. 118, tab. 26); in the ant-like flower of Chiloglottis cornuta;[[OV]] in the Mexican Bletia speciosa; and in the whole host of our remarkable European species of Ophrys: O. muscifera, O. apifera, O. aranifera, O. arachnites, &c. The taste for these splendidly flowering plants has so much increased, that the number of species cultivated by Messrs. Loddige, which, in 1813, was only 115, was upwards of 1650 in 1843, and in 1848, the number was estimated at no fewer than 2360. What a treasure of sumptuously flowering and unknown Orchideæ may be inclosed in the interior of Africa wherever there is an abundant supply of water! Lindley, in his beautiful work, On the Genera and Species of Orchideous Plants, 1840, counted exactly 1980 species; whilst Klotzsch at the close of the year 1848 counted 3545.
Whilst the temperate and cold zone possess only terrestrial Orchideæ, growing close to the ground, both forms, the terrestrial, as well as the parasitical, growing on the trunks of trees, are indigenous in the beautiful regions of the tropics. To the former class belong the tropical genera Neottia, Cranichis, and most Habenarias. But we have found both these forms as alpine plants on the declivity of the Andes of New Granada and Quito, viz., the parasitical (Epidendreæ) Masdevallia uniflora (at an elevation of 10,231 feet), Cyrtochilum flexuosum (at 10,103 feet), and Dendrobium aggregatum (at 9485 feet); and the terrestrial forms of Altensteinia paleacea, near Lloa Chiquito, at the foot of the volcano of Pichincha. Claude Gay is of opinion that the Orchideæ supposed to have been found growing on trees in the Island of Juan Fernandez and even at Chiloe, were probably only parasitical Pourretiæ, which advance as far south at least as 40°. In New Zealand, the tropical form of Orchideæ, hanging from trees, is still to be seen as far south as 45°. But the Orchideæ of Auckland and Campbell Islands (Chiloglottis, Thelymitra, and Acianthus), grow on level ground in moss. In the animal world there is at least one tropical form that penetrates further south. The Island of Macquarie (lat. 54° 39′) has an indigenous parrot, which lives therefore in a region nearer to the south pole than Danzig is to the north pole.[[OW]]
[92]. p. 226—“Form of the Casuarinæ.”
Acacias, in which the place of the leaves is supplied by phyllodia, Myrtaceæ (Eucalyptus, Metrosideros, Melaleuca, Leptospermum), and Casuarinæ, constitute the sole characteristics of the vegetable world of Australia (New Holland) and Tasmania (Van Diemen’s Land). Casuarinæ with their leafless, thin, thread-like, articulated branches, and their joints furnished with membranous, toothed spathes, have been compared by travellers,[[OX]] according to differences of species, either with arborescent Equisetaceæ (Horsetails) or with our Scotch firs. I have been much struck with the singular appearance of leaflessness presented by the small thickets of Colletia and Ephedra in South America, near the coast of Peru. Casuarina quadrivalvis penetrates, according to Labillardière, as far south as 43° in Tasmania. The mournful form of the Casuarina is not unknown in the East Indies and even on the eastern coast of Africa.
[93]. p. 227—“Acicular-leaved trees.”
The family of the Coniferæ (including the genera of Dammara, Ephedra, and Gnetum of Java and New Guinea, which are essentially allied to it, though distinctly separated by the form of the leaf and the whole conformation), plays so important a part in consequence of the number of individuals in each species, and by its geographical diffusion, while it covers in the northern temperate zone, as a social plant, such extensive districts, that we are almost compelled to wonder at the inconsiderable number of the species. We are not acquainted with so many Coniferæ by three-fourths as there are Palms already described, nay, the Coniferæ are numerically less than the Aroideæ. Zuccarini, in his “Contributions to the Morphology of the Coniferæ,”[[OY]] enumerates 216 species, of which 165 belong to the Northern and 51 to the Southern hemisphere. These proportional numbers must now, in consequence of my researches, be differently expressed, since, with the species of Pinus, Cupressus, Ephedra, and Podocarpus, which Bonpland and I discovered in the tropical part of Peru, Quito, New Granada, and Mexico, the number of the cone-bearing trees flourishing between the tropics amounts to 42. The excellent and latest work of Endlicher[[OZ]] contains 312 species of Coniferæ now living, and 178 of a primeval mundane period which are now buried in the coal formation, in variegated sandstone, in keuper, and in Jura limestone. The vegetation of the eocene world presents especially to us forms which, by their coëval relationship with several families of the present world, remind us that with it many intervening members have disappeared. The Coniferæ, so frequent in the primeval world, accompany, in particular, the ligneous remains of Palms and Cycadeæ; but in the most recent beds of lignite or brown coal we again find Coniferæ, our Pines and Firs, associated with Cupuliferæ (or Mastworts), Maples and Poplars.[[PA]]
If the surface of the earth did not rise to great altitudes within the tropics, the strikingly characteristic form of acicular-leaved trees would have remained wholly unknown to the inhabitants of that zone. I took great pains, in common with Bonpland, to trace out, in the Mexican Highlands, the lower and upper boundary line of the Coniferæ and Oaks. 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, because they announce a climate not yet invaded, as far as experience has hitherto shown, by that mortal disease called the black vomit (vomito prieto, a form of the yellow fever). For the oaks, especially the Quercus Xalapensis (one of the twenty-two Mexican species of oak which we first described), the lower line of vegetation, on the way from Vera Cruz to the capital of Mexico, somewhat below the Venta del Encero, is 3048 feet above the sea. At the western slope of the plateau, between the South Sea and Mexico, the inferior line for oaks is something lower; it begins near a hut named Venta de la Moxonera, between Acapulco and Chilpanzingo, at the absolute height of 2481 feet. I found a similar difference in the lower boundary line of the pine-forest. This boundary, towards the South Sea, in the Alto de los Caxones, north of Quaxinquilapa, is for the Pinus Montezumæ (Lamb.), which we at first had considered to be the Pinus occidentalis (Swartz), at the height of 4092 feet; but towards Vera Cruz, at the Cuesta del Soldado, it rises to 5979 feet. Both these kinds of tree, therefore, the oaks and firs as specified above, descended lower towards the Pacific than towards the Caribbean Gulf. During my ascent of the Cofre di Perote, I found the superior boundary Line of the oaks to be 10,353 feet; that of the Pinus Montezumæ 12,936 feet (about 2000 feet higher than the summit of Mount Ætna) and here, in February, considerable masses of snow had already fallen.
The greater the heights at which the Mexican cone-bearing trees begin to show themselves, the more singular is it, in the island of Cuba (where, at the border of the tropical zone the air, it is true, is cooled down during northerly winds to 46°.6 Fahr.), to see another kind of fir (P. Occidentalis, Swartz), in the plain itself, or on the gentle hills of the Isle of Pines, growing among palms and mahogany trees (Swietenia). Columbus even makes mention of a fir-wood (Pinal) in the journal of his first voyage (Diario del 25 de Nov., 1492), at Caya de Moya, north-east of Cuba. At Haiti, too (St. Domingo), the Pinus occidentalis near Cape Samana descends from the mountains down to the very beach. The stems of these firs, wafted by the gulf-stream to the two Azores, Graciosa and Fayal, were among the principal signs that proclaimed to the great discoverer the existence of unknown lands in the West.[[PB]] Is it positively ascertained that the Pinus occidentalis is entirely absent from Jamaica, notwithstanding its lofty mountains? We may be permitted to inquire also, what kind of Pinus grows on the eastern coast of Guatimala, since the P. tenuifolia (Benth.) is assuredly found only on the mountains near Chinanta.
On taking a general view of the species of plants which form the upper tree-boundary in the northern hemisphere from the frigid zone to the equator; I find, for Lapland, according to Wahlenberg, in the Sulitelma Mountains (lat. 68°), not acicular-leaved trees but birches (Betula alba), far above the upper limit of the Pinus sylvestris; and for the temperate zone I find in the Alps (lat. 45° 45′) Pinus picea (Du Roi), advanced beyond the birches. In the Pyrenees (lat. 42° 30′), we find Pinus uncinata (Ram.) and P. sylvestris, var. rubra; within the tropics in Mexico (lat. 19°–20°), Pinus Montezumæ extends far beyond Alnus toluccensis, Quercus spicata, and Q. crassipes; and in the snow-crowned mountains of Quito, beneath the equator, Escallonia myrtilloides, Aralia avicennifolia, and Drymis Winteri attain the highest limits. This last species of tree, identical with the Drymis granatensis (Mut.), and the Wintera aromatica of Murray, presents, as Dr. Joseph Hooker has shown,[[PC]] the most singular instance of the uninterrupted dissemination of the same species of tree from the southernmost part of Tierra del Fuego and Hermit Island, where it was discovered as early as 1577 by Drake’s expedition, up to the northern Highlands of Mexico, over a meridian extent of 86° of latitude or 5160 miles. Where the acicular or needle-leaved trees, as in the Swiss Alps and the Pyrenees, and not the birch as in the extreme north, form the boundary of arborescent vegetation on the loftiest mountains, which they picturesquely encircle, they are immediately followed in their ascent towards the snow-crowned summits, in Europe and Western Asia by the Alpine roses, Rhododendra, and at the Silla de Caracas, and the Peruvian Paramo de Saraguru, by the purplish-red blossoms of the graceful Befariæ. In Lapland the Rhododendron laponicum immediately follows the Coniferous trees; in the Swiss Alps, the Rhododendron ferrugineum and R. hirsutum, and in the Pyrenees the R. ferrugineum alone; and in the Caucasus the R. caucasicum. But R. caucasicum has also been found isolated by De Candolle in the Jura mountains (in the Creux de Vent), 5968 feet lower down, at the inconsiderable height of from 3303 to 3730 feet. If we would trace out the last zone of vegetation near the snow line we must name, according to our personal observation, in tropical Mexico, Cnicus nivalis and Chelone gentianoides; in the cold mountainous tracts of New Granada, the woolly Espeletia grandiflora, E. corymbosa, and E. argentea; in the Andes chain of Quito, Culcitium rufescens, C. ledifolium, and C. nivale;—yellow-blossomed Compositæ, which replace the somewhat more northerly lanose herbs of New Granada, and the Epeletiæ, with which they have so much physiognomical resemblance. This substitution or repetition of similar and almost identical forms in regions that are separated from each other by seas or wide intervening tracts, is a wonderful law of nature. It prevails even in the rarest forms of the floras. In Robert Brown’s family of the Rafflesiæ, separated from the Cytineæ, the two Hydnoræ in Southern Africa (H. Africana and H. Triceps), described by Thunberg and Drege, have, in South America, their counterpart in the H. Americana of Hooker.