Besides the height of their stems, the length, breadth, and position of the leaves and fruit, the form of the ramification aspiring or horizontal, and spreading out like a canopy or umbrella,—the gradations of colour, from a fresh green or silvery grey to a blackish-brown, all give to Coniferæ a peculiar physiognomy and character. The needles of Douglas’s Pinus lambertiana from North-west America are five French inches long; those of Pinus excelsa of Wallich, on the southern declivity of the Himalaya, near Katmandoo, seven French inches; and those of P. longifolia (Roxb.), from the mountains of Kashmeer, above a French foot long. In one and the same species the length of the leaves or needles varies in the most striking manner from the influence of soil, air, and elevation above the level of the sea. In travelling in an east and west direction through eighty degrees of longitude (above 3040 geographical miles), from the mouth of the Scheldt through Europe and the north of Asia to Bogoslowsk in the northern Ural and Barnaul beyond the Obi, I have found differences in the length of the needles of our common Fir (Pinus sylvestris) so great, that sometimes a traveller may be misled by the shortness and rigidity of the leaves, to think that he has discovered a new species allied to the Mountain Pine, P. rotundata (Link), P. uncinata (Ram.) Link has justly remarked (Linnæa, Bd. xv. 1841, S. 489) that such instances may be regarded as transitions to Ledebour’s P. sibirica of the Altai.
In the Mexican highlands I have looked with particular pleasure on the delicate cheerful green of the Ahuahuete, Taxodium distichum (Rich.), Cupressus disticha (Linn.), which, however, is much given to shedding its leaves. In this tropical region the above-mentioned tree, (of which the Aztec name signifies water-drum, from atl, water, and huehuetl, a drum, the trunk swelling to a great thickness), flourishes 5400 and 7200 (5755 and 7673 English) feet above the level of the sea, while in the United States of North America it is found in the low grounds of the cypress swamps of Louisiana, in the 43d parallel. In the Southern States of North America the Taxodium distichum (Cyprès chauve) reaches, as in the Mexican highlands, the height of 120 (128 English) feet, and the enormous thickness of 30 to 37 (32 to 39 English) feet, in diameter measured near the ground. (Emerson, Report on the Forests, pp. 49 and 101). The roots present the striking phenomenon of woody excrescences which project from 3 to 4½ feet above the earth, and are conical and rounded, and sometimes tabular. Travellers have compared these excrescences in places where they are very numerous to the grave tablets in a Jewish burying-ground. Auguste de St. Hilaire remarks with much acuteness:—“Ces excroissances du Cyprès chauve, ressemblant à des bornes, peuvent être regardées comme des exostoses, et comme elles vivent dans l’air, il s’en échapperoit sans doute des bourgeons adventifs, si la nature du tissu des plantes conifères ne s’opposoit au développement des germes cachés qui donnent naissance à ces sortes de bourgeons.” (Morphologie végétale, p. 91). A singularly enduring power of vitality in the roots of trees of this family is shown by a phenomenon which has excited the attention of vegetable physiologists, and appears to be of only very rare occurrence in other dicotyledonous trees. The remaining stumps of White Pines which have been cut down continue for several years to make fresh layers of wood, and to increase in thickness, without putting forth new shoots, leaves, or branches. Göppert believes that this only takes place by means of root nourishment received by the stump from a neighbouring living tree of the same species; the roots of the living individual which has branches and leaves having become organically united with those of the cut tree by their having grown together. (Göppert, Beobachtungen über das sogenannte Umwallen der Tannenstöcke, 1842, S. 12). Kunth, in his excellent new “Lehrbuch der Botanik,” objects to this explanation of a phenomenon which was known, imperfectly, so early as Theophrastus. (Hist. Plant. lib. iii. cap. 7, pp. 59 and 60, Schneider.) He considers the case to be analogous to what takes place when metal-plates, nails, carved letters, and even the antlers of stags, become enclosed in the wood of a growing tree. “The cambium, i. e. the viscid secretion out of which new elementary organs are constructed either of woody or cellular tissue, continues, without reference to the buds (and quite apart from them), to deposit new layers of wood on the outermost layer of the ligneous substance.” (Th. i. S. 143 and 166.)
The relations which have been alluded to, between elevation above the level of the sea and geographical and thermal latitude, manifest themselves often when we compare the tree vegetation of the tropical part of the chain of the Andes with the vegetation of the north-west coast of America, or with that of the shores of the Canadian Lakes. Darwin and Claude Gay have made the same remark in the Southern Hemisphere, in advancing from the high plains of Chili to Eastern Patagonia and Tierra del Fuego, where they found Drymis winteri and forests of Fagus antarctica and Fagus forsteri forming a uniform covering throughout long continuous lines running from north to south and descending to the low grounds. We find even in Europe small deviations (dependent on local causes which have not yet been sufficiently examined), from the law of constant ratio as regards stations or habitat of plants between elevation above the sea and geographical latitude. I would recall the limits, in respect to elevation, of the birch and the common fir in a part of the Swiss Alps, on the Grimsel. The fir (Pinus sylvestris) extends to 5940, and the birch (Betula alba) to 6480 French (6330 and 6906 English) feet; above the birches there is a higher line of Pinus cembra, whose upper limit is 6890 (7343 English) feet. Here, therefore, we have the birch intervening between two zones of Coniferæ. According to the excellent observations of Leopold Von Buch, and the recent ones of Martins, who also visited Spitzbergen, the following geographical limits were found in Lapland:—Pinus sylvestris extends to 70°; Betula alba to 70° 40´; and Betula nana quite up to 71°; Pinus cembra is altogether wanting in Lapland. (Compare Unger über den Einfluss des Bodens auf die Vertheilung der Gewächse, S. 200; Lindblom, Adnot. in geographicam plantarum intra Sueciam distributionem, p. 89; Martins, in the Annales des Sciences naturelles, T. xviii. 1842, p. 195).
If the length and arrangement of the needle-shaped leaves go far to determine the physiognomic character of Coniferæ, this character is still more influenced by the specific differences in the breadth of the needles, and the degree of development of the parenchyma of the appendicular organs. Several species of Ephedra may be called almost leafless; but in Taxus, Araucaria, Dammara (Agathis), and the Salisburia adiantifolia of Smith (Gingko biloba, Linn.), the surfaces of the leaves become gradually broader. I have here placed the genera in morphological succession. The specific names first chosen by botanists testify in favour of such a succession. The Dammara orientalis of Borneo and Java, often above ten feet in diameter, was first called loranthifolia; and Dammara australis (Lamb.) of New Zealand, which is 140 (149 English) feet high, was first called zamæfolia. In both these species of trees the leaves are not needles, but “folia alterna oblongo-lanceolata, opposita, in arbore adultiore sæpe alterna, enervia, striata.” The under surface of the leaves is thickly set with porous openings. This passage or transition of the appendicular system from the greatest contraction to a broad-leaved surface, like all progression from simple to compound, has at once a morphological and a physiognomic interest (Link, Urwelt, Th. I. 1834, S. 201-211). The short-stalked, broad, cleft leaf of the Salisburia (Kämpfer’s Gingko) has also its breathing pores only on the under side of the leaf. The original native country of this tree is unknown to us. By the connection and intercourse of Buddhistic communities it early passed from the temple-gardens of China to those of Japan.
In travelling from a port on the Pacific to Mexico, on our way to Europe, I witnessed the singular and painful impression which the first sight of a pine forest near Chilpanzingo made on one of our companions, who, born at Quito under the equinoctial line, had never seen needle trees, or trees with “folia acerosa.” It seemed to him as if the trees were leafless; and he thought that as we were travelling towards the cold North, he already recognised in this extreme contraction of the vegetable organs the chilling and impoverishing influence of the pole. The traveller whose impressions I here describe, whose name neither my friend Bonpland or myself can pronounce without regret, was Don Carlos Montufar (son of the Marquis of Selvalegre), an excellent young man, whose noble and ardent love of freedom led him a few years later, in the war of independence of the Spanish Colonies, to meet courageously a violent death, of which the dishonour did not fall on him.
[24] p. 26.—“The Pothos-form, Aroideæ.”
Caladium and Pothos are exclusively forms of the tropical world; the species of Arum belong more to the temperate zone. Arum italicum, A. dracunculus, and A. tenuifolium, extend to Istria and Friuli. No Pothos has yet been discovered in Africa. India has some species of this genus (Pothos scandens and P. pinnata) which are less beautiful in their physiognomy, and less luxuriant in their growth, than the American species. We discovered a beautiful and truly arborescent member of the group of Aroideæ (Caladium arboreum) having stems from 16 to 21 English feet high, not far from the convent of Caripe, to the East of Cumanas. A very curious Caladium (Culcasia scandens) has been discovered by Beauvois in the kingdom of Benin. (Palisot de Beauvois, Flore d’Oware et de Benin, T. i. 1804, p. 4, pl. iii.) In the Pothos-form the parenchyma is sometimes so much extended that the surface of the leaf is interrupted by holes as in Calla pertusa (Kunth), and Dracontium pertusum (Jacquin), which we collected in the woods round Cumana. The Aroideæ first led attention to the remarkable phenomenon of the fever-heat, which in certain plants is sensible by the thermometer during the development of their inflorescence, and which is connected with a great and temporary increase of the absorption of oxygen from the atmosphere. Lamarck remarked in 1789 this increase of temperature at the time of flowering in Arum italicum. According to Hubert and Bory de St. Vincent the vital heat of Arum cordifolium in the Isle of France was found to rise to 35°and 39° Reaumur, (110°.6 and 119°.6 Fahr.) while the temperature of the surrounding air was only 15°.2 R. (66°.2 F.) Even in Europe, Becquerel and Breschet found as much as 17½° difference, Reaumur (39°.4 Fahr.) Dutrochet remarked a paroxysm, an alternate decrease and increase of vital heat, which appeared to reach a double maximum in the day. Théodore de Saussure observed analogous augmentations of temperature, though to a less amount, only from 0°.5 to 0°.8 of Reaumur’s scale (1°.15 to 1°.8 Fahr.), in plants belonging to other families; for example, in Bignonia radicans and Cucurbita pepo. In the latter plant the use of a very sensitive thermoscope shews that the increase of temperature is greater in the male than in the female plant. Dutrochet, who previous to his early death made such meritorious researches in physics and in vegetable physiology, found by means of thermo-magnetic multiplicators (Comptes rendus de l’Institut, T. viii. 1839, p. 454, T. ix. p. 614 and 781) an increase of vital heat from 0°.1 to 0°.3 Reaumur, (0°.25 to 0°.67 Fahr.) in several young plants (Euphorbia lathyris, Lilium candidum, Papaver somniferum), and even among funguses in several species of Agaricus and Lycoperdon. This vital heat disappeared at night, but was not prevented by placing the plants in the dark during the day-time.
A yet more striking physiognomic contrast than that of Casuarineæ, Needle trees, and the almost leafless Peruvian Colletias, with Aroideæ, is presented by the comparison of those types of the greatest contraction of the leafy organs with the Nymphæaceæ and Nelumboneæ. We find in these as in the Aroideæ, leaves, in which the cellular tissue forming their surface is extended to an extreme degree, supported on long fleshy succulent leaf-stalks; as in Nymphæa alba; N. lutea; N. thermalis (once called N. lotus, from the hot spring of Pezce near Groswardein, in Hungary); the species of Nelumbo; Euryale amazonica of Pöppig; and the Victoria Regina discovered in 1837 by Sir Robert Schomburgk in the River Berbice in British Guiana, and which is allied to the prickly Euryale, although, according to Lindley, a very different genus. The round leaves of this magnificent water plant are six feet in diameter, and are surrounded by turned up margins 3 to 5 inches high, light green inside, and bright crimson outside. The agreeably perfumed flowers, twenty or thirty blossoms of which may be seen at the same time within a small space, are white and rose coloured, 15 inches in diameter, and have many hundred petals. (Rob. Schomburgk, Reisen in Guiana und am Orinoko, 1841, S. 233.) Pöppig also gives to the leaves of his Euryale amazonica which he found near Tefe, as much as 5 feet 8 inches French, or 6 English feet, diameter. (Pöppig, Reise in Chile, Peru und auf dem Amazonenstrome, Bd. ii. 1836, S. 432.) If Euryale and Victoria are the genera which present the greatest extension in all dimensions of the parenchyma of the leaves, the greatest known dimensions of a flower belong to a parasitical Cytinea, the Rafflesia Arnoldi (R. Brown), discovered by Dr. Arnold in Sumatra, in 1818: it has a stemless flower of three English feet diameter, surrounded by large leaf-like scales. Fungus-like, it has an animal smell, resembling beef.
[25] p. 26.—“Lianes, rope-plants, (‘Bush ropes;’ in Spanish, Vejuccos.”)
According to Kunth’s division of the Bauhinieæ, the true genus Bauhinia belongs to the New Continent: the African Bauhinia, B. rufescens, (Lam.) is a Pauletia (Cav.) a genus of which we found some new species in South America. So also the Banisterias, from among the Malpighiaceæ, are properly an American form; although two species are natives of India, and one species, Banisteria leona, described by Cavanilles, is a native of Western Africa. Within the tropics and in the Southern Hemisphere we find among the most different families of plants the twining rope-like climbers which in those regions render the forests at once so impenetrable to man, and on the other hand so accessible and habitable to the Quadrumanæ (or Monkeys) and to the Cercoleptes and the small tiger-cats. The rapid ascent to the tops of lofty trees, the passage from tree to tree, and even the crossing of streams by whole herds or troops of gregarious animals, are all greatly facilitated by these twining plants or Lianes.