Note 30 — PHYSIOGNOMY OF PLANTS.

p. 28.—“Willow Form.”

Of the leading representative of this form, the Willow itself, 150 different species are already known. They are spread over the northern hemisphere from the Equator to Lapland. They appear to increase in number and diversity of form between the 46th and 70th degrees of north latitude, and especially in the part of north of Europe where the configuration of the land has been so strikingly indented by early geological changes. Of Willows as tropical plants I am acquainted with ten or twelve species, which, like the willows of the southern hemisphere, are deserving of particular attention. As Nature seems as it were to take pleasure in multiplying certain forms of animals, for example Anatidæ (Lamellirostres) and Columbæ, in all the zones of the earth; so are Willows, the different species of Pines, and Oaks, no less widely disseminated: the latter (oaks) being always alike in their fruit, though much diversified in the forms of their leaves. In Willows, the similarity of the foliage, of the ramification, and of the whole physiognomic appearance, in the most different climates, is unusually great,—almost greater than even in Coniferæ. In the southern part of the temperate zone of the northern hemisphere the number of species of willows decreases considerably, yet (according to the Flora atlantica of Desfontaines) Tunis has still a species of its own resembling Salix caprea; and Egypt reckons, according to Forskäl, five species, from the catkins of whose male flowers a medicine much employed in the East, Moie chalaf (aqua salicis) is obtained by distillation. The Willow which I saw in the Canaries is also, according to Leopold von Buch and Christian Smith, a peculiar species, common however to that group and to the Island of Madeira,—S. canariensis. Wallich’s Catalogue of the plants of Nepaul and of the Himalaya cites from the Indian sub-tropical zone thirteen species, partly described by Don, Roxburgh, and Lindley. Japan has its indigenous willows, one of which, S. japonica (Thunb.) is also found as a mountain plant in Nepaul.

Previous to my expedition, the Indian Salix tetrasperma was the only known intertropical species, so far as I am aware. We collected seven new species, three of which were from the elevated plains of Mexico, and were found to extend to an elevation of 8000 (about 8500 English) feet above the level of the sea. At still greater elevations,—for example, on the mountain plains situated between 12000 and 14000 feet, (about 12790 and 14920 English,) which we often visited,—we did not find, either in the Andes of Mexico or in those of Quito and Peru, anything which could recall the small creeping alpine willows of the Pyrenees, the Alps, and Lapland (S. herbacea, S. lanata, and S. reticulata). In Spitzbergen, where the meteorological conditions have much analogy with those of the Swiss and Scandinavian snow-mountains, Martins described two dwarf willows, of which the small woody stems and branches creep on the ground, and which lie so concealed in the turf-bogs that their small leaves are only discovered with difficulty under the moss. The species found by me in Peru in 4° 12´ S. latitude, near Loxa, at the entrance of the forests where the best Cinchona bark is collected, and described by Willdenow as Salix humboldtiana, is the one which is most widely distributed in the western part of South America. A sea-shore species, S. falcata, which we found on the sandy coast of the Pacific, near Truxillo, is, according to Kunth, probably only a variety of the above; and possibly the fine and often pyramidal willow which accompanied us along the banks of the Magdalena, from Mahates to Bojorque, and which, according to the report of the natives, had only extended so far within a few years, may also be identical with Salix humboldtiana. At the confluence of the Rio Opon with the Magdalena, we found all the islands covered with willows, many of which had stems 64 English feet high, but only 8 to 10 inches in diameter. (Humboldt and Kunth, Nova Gen. Plant. T. ii. p. 22, tab. 99.) Lindley has made us acquainted with a species of Salix from Senegal, and therefore in the African equinoctial zone. (Lindley, Introduction to the Natural System of Botany, p. 99.) Blume also found two species of Salix near the equator, in Java: one wild and indigenous, S. tetrasperma; and another cultivated, S. sieboldiana. From the southern temperate zone I know only two willows described by Thunberg, (S. hirsuta and S. mucronata); they grow by the side of Protea argentea (which has itself very much the physiognomy of a willow), on the banks of the Orange River, and their leaves and young shoots form the food of the hippopotamus. Willows are entirely wanting in Australia and the neighbouring islands.