688 GEOGRAPHICAL AND GEOLOGICAL BOTANY. 



The savannahs and llanos are plains or plateaux covered with grass, with 

 few trees, and sometimes deserts. 



16. Region oftJie Mexican Highlands (Bonpland's Region). 



Altitude, above 5000 feet. Mean temperature, C7-79 Fahr. (20-27 C.). 



Character. The climate of the Mexican Highlands is very uniform. 

 Tropical forms vanishing or decreasing : Tree-ferns, Palmaceae, Piperaceae, 

 Euphorbiaceae, Melastoniaceae, Passifloraceae. Extratropical forms make 

 their appearance or become more abundant : Amentacess (Salix, Quercus), 

 Coniferse (Pinus, Cupressus), Labiatae (Salvia, Stachys, Marrubium), 

 Pedicularis, Anchusa, Myosotis, Polemoniura, Ericaceae (Vaccinium, Ar- 

 butus, Arctostaphylos), Compositae (greatly increasing),Valeriana, Galium, 

 Cornus, Caprifolium, Umbelliferae, Rosaceae (Amygdalus, Mespilus, 

 Rosa, Potentilla), Caryophylleae (Arenaria), Cruciferse (Draba), Ranun- 

 culacese (Anemone, Ranunculus). 



Characteristic genera. Mirabilis, Maurandya, Leucophyllum, Holtzia, 

 Dahlia, Zinnia, Schkuhria, Ximenesia, Lopezia, Vauquelinia, Choisya, 

 Cheirostemon. 



Predominant trees and shrubs. Forests of Oaks and Conifers. Pinus 

 occidentals, Abies hirtella, Cupressus thurifera, C. sabinoides, Taxodium 

 distichum, Quercus (16 sp.), Salix Bonplandiana, S. paradoxa, &c., Arbu- 

 tus mollis, A. petiolaris, Arctostaphylos polifolia, A. pungens, c., Vac- 

 cinium geminiflorum, V. stamineum, V. confertum, Rosa Montezumae, 

 Mespilus pubescens, Amygdalus microphylla, Cheirostemon platanoides. 



Cultivated plants. Maize, European cereals, Olives and fruits, and es- 

 pecially Agave americana. 



Note. In the uppermost regions of the mountains the flora acquires an 

 alpine aspect. Here occur Cyperus toluccensis, Chelone gentianoides, 

 Cnicus nivalis, Ageratum arbutifolium, Senecio (many procumbent spe- 

 cies), Potentilla ranunculoides, Lupinus elegans, L. montana, Arenaria 

 bryoides. 



(For the geographical botany of this and adjacent districts the volume 

 preparing by Mr. Hemsley for Messrs. Salvin and Godman's ' Natural 

 History of Mexico and Central America ' will be most important.) 



17. Region of Cinchonas (Andes, or Humloldfs Region). 



Altitude, 5000-9000 feet. Mean temperature, 59-68 Fahr. (15-20 C.) . 



Character. The tropical Andean region of Grisebach. The Pacific 

 slope is very sudden, the coast being nearly rainless and the vegetation 

 poor. On the eastern slope of the Cordilleras a long summer rainy season 

 is very favourable to forest vegetation, among which the Cinchona-yield- 

 ing trees may be specially mentioned. Extratropical forms make their 

 appearance, or become more frequent : Graminaceas, Amentacese (Quer- 

 cus, Salix), Labiatse (Salvia, Stachys, Scutellaria), Anchusa, Myosotis, 

 Swertia, Ericacea3, Compositaa (very numerous), Caprifoliaceae (Viburnum, 

 Sambucus), Umbelliferae (Ferula, Ligusticum), Rosaceae, Cruciferae, 

 Ranunculaceae. On the other hand, certain tropical forms vanish or be- 

 come rarer, but a few particular species of Palmas, Piperaceae, Cactaceae, 

 PassifloreaB, and Melastomaceae ascend to a considerable altitude. 



