670 GEOGEAPHICAL AND GEOLOGICAL BOTANY. 



Rafflesia, with its flowers 8 feet in diameter ; while in America this is 

 almost rivalled by the Victoria Water-lily, and the Aristolochias with 

 their enormous helmet-like flowers said, indeed, to be worn in sport as 

 caps by the Indian boys. 



Rich as the vegetation of this zone is in general, we find within the 

 limits some of the poorest tracts upon the globe namely, where water is 

 wanting. The African desert and a portion of Arabia are the most striking 

 examples ; but the llanos of Venezuela are scarcely less parched and life- 

 less during the dry season, and in the rainy season present only grassy 

 plains like the steppes of Central Asia. The poverty of these tracts is 

 accounted for by their peculiar position, cutting them off from the in- 

 fluence of moist currents of air, their natural waterless condition being 

 of course dependent on the geological changes which gave them their 

 present configuration. 



2. The Tropical Zones. These extend, in the north and south hemi- 

 spheres, from the boundaries of the equatorial zone, at the isotherms of 

 79-3 F. (26 0.), to the isotherms of 72*5 F. (22 0.) . Taken altogether, 

 the characteristics of these zones, as might be expected, are closely allied 

 to those of the preceding. Rio de Janeiro and Canton are cited by Meyen 

 as instances of this resemblance j Palms, Bananas, Cannaceae, Meliaceae, 

 Anonaceae, and Sapindaceae prevail (in humid districts) here, and Orchids, 

 Pothos-like plants, and Lianes abound. The Tree-Ferns, the Pepper- 

 plants, Melastomaceae, and Convolvulaceae, however, become more pro- 

 minent here, and serve as distinctive characters ; and it is stated that, in 

 these zones, the forests exhibit fewer parasites and more underwood. , 

 That portion of the western coast of South America lying within the 

 south tropical zone forms an exception to the general rule of luxuriance 

 of vegetation, as does the inland tract of Africa bordering on the equa- 

 torial zone. 



3. The Subtropical Zones. These are bounded on the equatorial side by 

 the annual isotherm of 72'5 F. (22 C.), and towards the poles by the 

 isotherms of 68 F. (20 C.). The countries lying within these enjoy the 

 most delightful climates on the globe. Though the summer heat never 

 rises to the intense heat of the torrid zone, it suffices to ripen most of the 

 tropical fruits ; while the winters are so mild that vegetation is never 

 arrested. Palms and Bananas are still met with in the plains, and 

 arborescent Grasses form a feature of the landscape, both in America 

 and Asia ; but the most striking character of these regions is formed 

 by the abundance of forest-trees having broad, leathery, and shining 

 leaves, such as the Magnolias and the Lauraceae, and also of the plants 

 of the Myrtle tribe. Proteaceae, Acacias, and Heaths attain their 

 maximum development. 



4. The Warmer Temperate Zones. Equatorial boundaries, the annual 

 isotherms of 68 F. (20 C.) j polar boundaries, the isotherms of 54 -5 F. 

 (say 12 C.). The general characteristics of these zones arise from the 

 combination of the shining, leathery-leaved trees of the subtropical zones 

 with the forest-trees which we find in our own country, such as Oaks, 

 Beeches, &c. ; the Palms vanish ; -but a number of handsome evergreen 

 shrubs present themselves, and Heaths, Cisti, and showy Leguminous 

 plants are very abundant. The countries lying within these zones in 



