The black twigs of the buffalo-thorn (_Acacia latronùm_), a low shrub abounding in northern Ceylon, are beset at every joint by a pair of thorns set opposite each other, like the horns of an ox, as sharp as a needle, from two to three inches in length, and thicker at the base than the stem they grow on; and the Acacia tomentosa, another member of the same numerous genus, has thorns so large as to be called the jungle-nail by Europeans, and the elephant-thorn by the natives. In some of these thorny plants, the spines grow, not singly, but in branching clusters, each point presenting a spike as sharp as a lancet; and where these shrubs abound, they render the forest absolutely impassable, even to animals of the greatest size and strength. The formidable thorny plants of the torrid zone, which are often made use of by man to protect his fields and plantations against wild beasts and robbers, have sometimes even been made to serve as a bulwark against hostile invasions. Thus Sir Emerson Tennent informs us, that, during the existence of the Kandyan kingdom, before its conquest by the British, the frontier forests were so thickened and defended by dense plantations of thorny plants as to form a natural fortification impregnable to the feeble tribes on the other side; and at each pass which led to the level country, movable gates, formed of the same thorny beams, were suspended as an ample security against the incursions of the naked and timid lowlanders. [Illustration: THE LUM TREE.] Poets and moralists, judging by what they see in England, have concluded that fruits of a small size, whose fall cannot be dangerous to man, invariably grow on high trees, while large fruits, such as the pumpkin, are only found trailing on the ground. But a visit to the tropics would soon convince them of their error, for two of the largest and heaviest fruits known, the Brazilian nut (_Bertholletia_) and the Durian of the Indian Archipelago, grow on high forest trees, from which they fall down when ripe, and frequently wound or kill the natives. ‘From this,’ says Mr. Wallace, ‘we can learn two things--in the first place, not to draw general conclusions from a locally very limited knowledge of nature, and, secondly, that trees and fruits, as well as the manifold productions of the animal kingdom, have not been exclusively organised with a reference to man.’ [Illustration: A CEYLONESE COCOA-NUT OIL-MILL.] CHAPTER XIII. PALMS AND FERNS.