•270 OUTLINE OF PLANT GEOGRAPHY 



of perpetual snow. The first pines appear at 2,200 metres, and the 

 oaks reach toaboul 3,400 m., above which for another 1,000 metres 

 a Dumber of conifers extend. Above this forest, is an alpine region 

 where the vegetation is composed of coarse grasses, and a variety 

 of shrubby and half shrubby plants, especially Compositae, 

 Labiatae, Rosaceae, etc., as well as some herbaceous species, 

 grasses, sedges, Compositae, and others, all decidedly boreal 



types. 



In the upper forest, the epiphytic orchids and Tillandsias of the 

 lower elevations, give place to mosses and lichens. 



The western coast of Mexico is much drier, and the tropical 

 forest Less developed. Pines and other northern forms grow at 

 lower elevations than in the eastern part of the country. 



Central America, 1 Nicaragua, Honduras, Guatemala and Costa 

 Rica in the character of their vegetation are intermediate between 

 Mexico and equatorial South America. There is a gradual dis- 

 appearance of the oaks, pines, and other northern genera char- 

 acteristic of the Mexican highlands, and an increasing number of 

 palms, and other tropical types. As might be expected, the boreal 

 genera ascend to higher elevations as the latitude diminishes, and 

 finally disappear completely in the equatorial forests of Panama 

 and South America. 



As in Mexico, the Pacific slope of Central America is much 

 drier than the Atlantic coast, but nevertheless supports a forest, 

 mostly of tropical species, up to an elevation of about 3,000 feet. 

 Above this tropical forest belt are open savannas, and still higher, 

 forests of pines. 



The eastern slope is covered with a heavy rain-forest, in which 

 palms form a very conspicuous feature, these belonging to such 

 tropical South American genera as Bactris, Geonoma, Iriartia. 

 The central plateau in the more southern part, at an elevation 

 of about 5,000 feet, supports a forest in which many trees like the 

 silk-cotton and Spanish cedar are leafless during the dry season. 



The forests of Costa Rica are notable for the great profusion 

 of ferns and orchids, this being one of the richest regions for these 

 plants known to the botanist. Palms, tree-ferns, Scitamineae 

 (Canna, gingers, etc.), are very abundant as they are everywhere 

 in the tropical American rain-forests. 



1 Drude, loc. cit., p. 509. 



