All along the Mexican Gulf stretches a broad zone of lowlands, called the _tierra caliente_, or hot region, which has the usual high temperature of the tropics. Parched and sandy plains, dotted with mimosas and prickly opuntias, are intermingled with savannahs, and woodlands of exuberant fertility. The branches of the stately forest trees are festooned with clustering vines of the dark purple grape, convolvuli, and other flowering parasites of the most brilliant dyes. The undergrowth of prickly aloe, matted with wild rose and honeysuckle, makes in many places an almost impervious thicket. In this wilderness of sweet-smelling buds and blossoms flutter birds of the parrot tribe, and clouds of butterflies, whose colour, nowhere so gorgeous as here, rival those of the vegetable world; while birds of exquisite song,--the scarlet cardinal, and the mocking-bird that comprehends in his own notes the whole music of a forest,--fill the air with melody. [Illustration: CARDINAL.] [Illustration: MOCKING-BIRD.] But, like the genius of evil, the malaria engendered by the decomposition of rank vegetable substances in the hot and humid soil, poisons these enchanting retreats, and from the spring to the autumnal equinox renders them dangerous or fatal to man. Hastening to escape from its influence, the traveller, after passing some twenty leagues across the dreaded region of the yellow-fever, finds himself rising into a purer atmosphere. His limbs recover their elasticity. He breathes more freely, for his senses are not now oppressed by the sultry heats and intoxicating perfumes of the lowlands. The aspect of nature, too, has changed, and his eye no longer rests on the gay variety of colours with which the landscape was painted there. The vanilla, the indigo, the chocolate-tree disappear as he advances, but the sugar-cane and the glossy-leaved banana still remain; and when he has ascended about four thousand feet, he sees, in the unchanging green and the rich foliage of the liquidambar-tree, that he has reached the height where clouds and mists settle in their passage from the Mexican Gulf, and keep up a perpetual moisture.