Note 18 — PHYSIOGNOMY OF PLANTS.

p. 22.—“The Mimosa form.”

The finely feathered or pinnated leaves of Mimosas, Acacias, Schrankias, and species of Desmanthus, are most truly forms of tropical vegetation. Yet there are some representations of this form beyond the tropics; in the northern hemisphere in the Old Continent I can indeed cite but one, and that only in Asia, and a low-growing shrub, the Acacia Stephaniana, according to Kunth’s more recent investigations a species of the genus Prosopis. It is a social plant, covering the arid plains of the province of Shirwan, on the Kur (Cyrus), as far as the ancient Araxes. Olivier also found it near Bagdad. It is the Acacia foliis bipinnatis mentioned by Buxbaum, and extends as far north as 42° of latitude. (Tableau des Provinces situées sur la Côte occidentale de la Mer Caspienne, entre les fleuves Terek et Kour, 1798, pp. 58 and 120.) In Africa the Acacia gummifera of Willdenow advances as far as Mogador, or to 32° north latitude.

On the New Continent, the banks of the Mississipi and the Tennessee, as well as the savannahs of Illinois, are adorned with Acacia glandulosa (Michaux), and A. brachyloba (Willd). Michaux found the Schrankia uncinata extend northwards from Florida into Virginia, or to 37° N. latitude. Gleditschia tricanthos is found, according to Barton, on the east side of the Alleghany mountains, as far north as the 38th parallel, and on the west side even as far as the 41st parallel. Gleditschia monosperma ceases two degrees farther to the south. These are the limits of the Mimosa form in the northern hemisphere. In the southern hemisphere we find beyond the tropic of Capricorn simple leaved Acacias as far as Van Diemen Island; and even the Acacia cavenia, described by Claude Gay, grows in Chili between the 30th and 37th degrees of south latitude. (Molina, Storia Naturale del Chili, 1782, p. 174.) Chili has no true Mimosa, but it has three species of Acacia. Even in the north part of Chili the Acacia cavenia only grows to a height of twelve or thirteen feet; and in the south, near the sea coast, it hardly rises a foot above the ground. In South America, north of the equator, the most excitable Mimosas were (next to Mimosa pudica), M. dormiens, M. somnians, and M. somniculosa. Theophrastus (iv. 3) and Pliny (xii. 10) mention the irritability of the African sensitive plant; but I find the first description of the South American sensitive plants (Dormideras) in Herrera, Decad. II. lib. iii. cap. 4. The plant first attracted the attention of the Spaniards in 1518, in the savannahs on the isthmus near Nombre de Dios: “parece como cosa sensible;” and it was said that the leaves (“de echura de una pluma de pajaros”) only contracted on being touched with the finger, and not if touched with a piece of wood. In the small swamps which surround the town of Mompox on the Magdalena, we discovered a beautiful aquatic Mimosacea (Desmanthus lacustris). It is figured in our Plantes équinoxiales, T. i. p. 55, pl. 16. In the Andes of Caxamarca we found two Alpine Mimoseæ (Mimosa montana and Acacia revoluta), 8500 and 9000 French (about 9060 and 9590 English) feet above the surface of the Pacific.

Hitherto no true Mimosa (in the sense established by Willdenow), or even Inga, has been found in the temperate zone. Of all Acacias, the Oriental Acacia julibrissin, which Forskål has confounded with Mimosa arborea, is that which supports the greatest degree of cold. In the botanic garden of Padua there is in the open air a tree of this species with a stem of considerable thickness, although the mean temperature of Padua is below 10.°5 Reaumur (55°.6 Fahr.)