FLORA OF THE TROPICAL ZONE. 471 



of the Pacific side of the country is altogether different from the 

 Atlantic side. The forest trees of the Rocky Mountain region 

 include about 50 species, many of which are tree-like shrubs. 

 Reaching into the Mexican region are the Yucca brevifolia, the giant 

 Cactus, a species of Pinus, Arbutus, Fraxinus, Platanus, and 

 Quercus. A desert willow, Chilopsis, fringes the watercourses. A 

 Texas mulberry, Morus, extends into Arizona. Among conifers the 

 yellow pine, Pinus contorta, covers large areas. It is associated with 

 various other pines, such as the nut pine, fox-tail pine, white pine, 

 the Douglas spruce, and a species of Juniper known as red cedar. 

 The mountain mahogany, Cercocarpus, is peculiar to the great basin, 

 but the ash-leafed maple, which yields sugar from the sap, reaches 

 to Canada and New England. The poplars, generally known as 

 Cotton-woods and Balsam poplars, rather belong to the arid regions, 

 where streams issue from the mountains. Oaks are conspicuously 

 absent. 



Tropical Zone. The tropical type of life was separated at an an- 

 cient period into American and Asiatic portions. It is characterised by 

 its gigantic Monocotyledons and Arborescent Polypetalse. 1 Some of the 

 palms of the Amazon have a height of one to two hundred feet, and 

 some, like Raphia and Maximiliana, have leaves more than 50 feet long. 

 The distinctive features of tropical forests are the tall trunks, with a 

 crown of foliage shutting out the light, and descending aerial roots 

 like buttresses. The silk-cotton trees are thus characterised. Below 

 the tall forest trees is a growth of lower trees, rising to 40 or 50 

 feet, and below these dwarf palms, tree ferns, and herbaceous ferns. 

 The ground is sometimes carpeted with club mosses and small 

 flowering plants. The palms include creepers like Calamus, which 

 grows to a length of thousand feet, and yields the rattan. The rattan 

 canes abound in the Malay Archipelago. One of them yields the 

 dragon's blood ; another palm yields the sago ; the Arenga or sugar 

 palm, and the Areca are both Malayan types. Other characteristic 

 tropical forms of plant life are mangroves, bamboos, screw pines, 

 bananas, arums, sensitive mimosas, and among orchids the Oneidiums 

 of the flooded Amazon, the Cselogynes of the swamps, and the 

 Cattleyas, of the drier forest ; the ginger-worts, which produce 

 ginger, cardamoms, grains of paradise and turmeric, begonias, vanilla, 

 and a multitude of ferns. Among the characteristic trees many have 

 the trunk covered with flowers, such as the cocoa tree, and Polyalthea, 

 one of the custard apples in Borneo. Tropical trees yield the drugs 

 toulu, camphor, benzoin, catechu, cajuput oil, ' gamboge, quinine, 

 angostura bark, quassia, the urari poison, and the upas poison. 

 Among spices are cloves, cinnamon, and nutmeg. Among fruits^ 

 brazil nuts, tamarinds, guavas, cocoa, bread-fruit, the avocado pear, 

 custard apple, durian, mango, mangosteen, soursop, and papaw, which 

 are all exogenous. Among the tropical exogenous woods are 

 mahogany, teak, sandal wood, and trees which yield log wood, brazil 

 wood, sappan wood, iiidia rubber, gutta percha, gum tragacanth, gum 

 1 Wallace, "Tropical Nature," 1878 ; and Henfrey's "Botany," by Masters. 



