531 THE TROPICAL WORLD. 



like, from the trees, on which they are parasitically rooted. The Opuntias arc unsym- 

 metrically constructed of thick, flat joints springing one from the other, while the 

 melon-shaped Echinocacti and Mammillarae, longitudinally ribbed or covered with 

 warts, remain attached to the soil. The dimensions of these monstrous plants are ex- 

 ceedingly variable. One of the Mexican echinocacti (E. Visnaga) measures four 

 feet in bight, three in diameter, and weighs about two hundred pounds ; while the 

 dwarf-cactus (E. nana) is so small that, loosely rooted in the sand, it frequently re- 

 mains sticking between the toes of the dogs that pass over it. The splendid purple 

 flowers of the cactuses form a strange contrast to the deformity of their stems, and the 

 spectator stands astonished at the glowing life that springs forth from so unpromising 

 a stock. These strange compounds of ugliness and beauty are in many respects useful 

 to man. The pulp of the melocacti, which remains juicy during the driest season of 

 the year, is one of the vegetable sources of the wilderness, and refreshes the traveler 

 after he has carefully removed the thorns. Almost all of them bear an agreeable acid 

 fruit, which, under the name of the Indian fig, is consumed in large quantities in the 

 West Indies and Mexico. The light and incorruptible wood is admirably adapted for 

 the construction of oars and many other implements. The farmer fences his garden 

 with the prickly opuntias ; but the services which they render, as the plants on which 

 the valuable cochineal insect feeds and multiplies, are far more important. 



The cactuses prefer the most arid situation, naked plains, or slopes, where they are 

 fully exposed to the burning rays of the sun, and impart a peculiar physiognomy to a 

 great part of tropical America. None of the plants belonging to this family existed 

 in the Old World previously to the discovery of America ; but some species have 

 since then rapidly spread over the warmer regions of our hemisphere. The Nopal 

 (Cactus opuntia) skirts the Mediterranean along with the American agave, and 

 from the coasts has even penetrated far into the interior of Africa, everywhere main- 

 taining its ground, and conspicuously figuring among the primitive vegetation of the 

 land. Although chiefly tropical, the cactuses have a perpendicular range, which but 

 few other families enjoy. From the low sand-coasts of Peru and Bolivia they ascend 

 through vales and ravines to the highest ridges of the Andes. 



What a contrast between these deformities and the delicately feathered Mimosas, 

 unrivaled among the loveliest children of Flora in the matchless elegance of their 

 foliage ! Our acacias give but a faint idea of the beauty which these plants attain 

 under the fostering rays of a tropical sun. In most species the branches extend hori- 

 zontally, or umbrella-shaped, somewhat like those of the Italian pine, and the deep- 

 blue sky shining through the light green foliage, whose delicacy rivals the finest em- 

 broidery, has an extremely picturesque effect. Endowed with a wonderful sensibility, 

 many of the mimosas seem, as it were, to have outstepped the, bounds of vegetable 

 life, and to rival in acuteness of feeling the coral polyps and the sea-anemones of the 

 submarine gardens. The Porliera hygrometrica foretells serene or rainy weather by 

 the opening or closing of its leaves. Large tracts of country in Brazil are almost 

 entirely covered with sensitive plants. The tramp of a horse sets the nearest ones in 

 motion, and, as if by magic, the contraction of the small gray-green leaflets spreads in 

 quivering circles over the field, making one almost believe, with Darwin and Dutro- 

 chet, that plants have feeling 



Among the most remarkable forms of tropical vegetation, the creeping plants, bush- 



