The north and south of America have the same length of day; but in the seasons which depend not merely on astronomical but on a variety of local causes, the analogy does not hold and very remarkable discrepancies appear. Thus, for example, the east coast of Brazil has the rainy Season from March to September, while Peru, lying under the very same latitude, has it from November to March. Within the tropics the transition from the rainy to the dry season takes place almost instantaneously; but in receding from the tropics on either side the change of seasons becomes more and more gradual till at last, in the polar zones, nature, bound in icy chains, affords for living existence only a short awakening out of a long winter sleep.
Consult publications of the United States Weather Bureau, the Canadian Meteorological Office and the Mexican Weather Service; Greely's 'American Weather) (1888).
Flora.— The sections of cultivation have been dealt with already, and we shall consider here only the indigenous features. From north to south the general succession is as follows: The surface-thawed Arctic tundra bears only reindeer-moss, blossoming weeds in its brief hot summer, and dwarf willows. From about the Arctic Circle to the southern coast of Alaska, James Bay and the North Sackatche wan, we find shrubby plants, most of them yielding berries; then the universal wood-of all-work, the famed (Alaska spruce," with clumps of birch and alder: these at first sparsely, then forests of larger spruces, pine, hemlock and fir. This coniferous growth extends in enormous volume down the cool, wet Pacific slope to central California; the giant redwoods and sugar-pines, etc., and the huge sequoia, the largest and oldest plant on the earth, being famous everywhere. East ern Canada is forested with similar coniferous species; so is the United States through Michi gan, Wisconsin and west to Minnesota, to southern Missouri and northwestern Arkansas, and to northeastern Texas and the Indian Ter ritory. The central United States has predom inant deciduous (hardwood) trees, such as the oak of many varieties, the beech, maple, elm, chestnut, black walnut, hickory, ironwood, pepperage, red mulberry, etc. In the southern States the yellow pine holds foremost place. The characteristic forms of the Southern States are the magnolia, palmetto, tulip-tree, plant-tree, pecan, etc., with the cypress everywhere in the swamps. The Cordilleran woods are chiefly conifers on the mountains; on the plains and in the valleys are the yucca, cactus, etc., whose dense, thorny growth is termed chaparral. The
wild picturesqueness and even grotesqueness of the cactus forms is noted; and it furnishes food for animals that would otherwise starve on the arid steppes. The north Mexican plateau has little wood except on the mountains. South ward vegetation blends with the tropical forms, and in Central America and the Antilles the most valuable trees are the mahogany and box wood, and of vegetable products vanilla and ginger.
In South America there is no Arctic region; but the great differences in altitudes and the water supply give it a wide range of native production. The immense rainfall and steady tropic heat of the north shore along the Carib bean and in the Magdalena Valley create a pro fuse tropical flora on the lowlands, changing to palms, bamboos, tree-ferns, etc., on the higher levels, and coniferous trees on the mountains. Along the Orinoco the llanos, plains with im mensely tall grasses and great single trees, take the place of forests. The vast selvas or swamp forests of the Amazon occupy the heart of the continent. These colossal tropic jungles, often formed into an almost impenetrable web by multitudes of creeping and climbing plants, con tain an almost unexploited variety of magnifi cent trees with the most beautiful ornamental woods,— as rosewood, cocabola, etc.,— products like india-rubber, brazilwood for dyeing, cin chona for medicine, etc. Dense forests of cinchona overshadow the mountain terraces of Quito. South of the selvas are the forests of Mat to Grosso, the great Brazilian province east of Bolivia; south of this again, and of the Bolivian Cordillera, is the Gran Chaco, or ((great round up," from the Paraguay to the Andes,—a region of three to five hundred thousand square miles, largely plains, but with heavy forests including the wax-palm, and with tree-like thistles on the lower plains. Now begin the pampas of the lower La Plata, which are fine grassy plains in the northern part, but in south Argentina and Patagonia become semi-arid steppes. The west ern strip has already been dealt with.
Consult Gray's 'Synoptical Flora of North America' (1886-97) ; Heller's 'Catalogue of North American Plants North of Mexico' (1900 ; Sargent's 'Silva of North America' (1890-91) ; Britton and Brown's 'Illustrated Flora of the Northern United States, Canada and the British Possessions' (1896-98) ; Berg's (Physiognomy of Tropical Vegetation in South America' (1894) ; Rusby's 'Enumeration of Plants Collected in South America' (in Torrey Botanical Club Bulletin, Vols. XV, XX, XXII, XXV, XXVII).