ALTITUDINAL DISTRIBUTION OF OECHIDS. 301 



grass, Pennisetum distachyum, which grows fifteen to twenty feet high ; an infinite 

 variety of Begoniae and Apocynaceae growing in tufts on the water's edge, interspersed 

 with terrestrial orchids such as Habenaria spathacea, II. diffusa, H. lactiflora, Ponthieva 

 oblongifolia, and Spiranthes saccata. 



Associated with these shrubby and herbaceous elements are many lofty trees 

 belonging to the Leguminosae, Sapotaceae, Combretaceae, Malpighiaceae, Meliaceae, &c, 

 clothed with a variety of epiphytes of the genera Pothos and Begonia and numerous 

 orchids, among them Stanhopea tigrina, 8. saccata, Maocillaria aromatica, Epidendrum 

 ancipticaulon, E. rigidum, E. candollei, Pleurothallis microphylla, Oncidium sphacela- 

 tion, 0. stramineum, Coelia baueriana, Zygopetalum grandiflorum, and Pcmera striata. 



This rich and varied vegetation constitutes a region quite different from that of the 

 coast, and it may be designated the warm temperate region of the ravines. 



The districts situated between 3250 and 4000 feet of absolute height present an 

 intermixture of the plants of the hot humid regions and those of regions enjoying a 

 much lower temperature. Thus even at elevations of about 3000 feet, oaks begin to 

 appear, whereas the gigantic Per sea gratissima of lower altitudes ceases to show itself, 

 and the sapodilla, papaw, and large species of fig become rare, while ferns, Rubiaceae, 

 Symplocos, Turpinia insignis, Berberis tenuifolia, and Gesneraceae abound. 



2. The Temperate Begion. — The great temperate region of the eastern side of the 

 Cordilleras of Mexico may be divided into three subregions, the whole of which con- 

 stitutes a zone situated between 3000 and 5900 feet, or even up to 6500 feet of absolute 

 height. 



First Subregion : Warm Temperate. — This is situated on the confines of the tropical 

 regions, and retains certain elements of the same vegetation, associated, however, with 

 a large number of different species, many of which ascend to altitudes of 6500 feet. 

 It is specially characterized by its oak-forests, composed of several species, various 

 Gentianaceae, Zamia, Buyschiu, and Orchideae. Promineut among the last are numerous 

 species of Stanhopea, Brassavola glauca, Cyrtochilum maculatum, Epidendrum radiatum, 

 E. parkinsonianum, and other species which grow on the bark of the oak trees. 

 Cypripedium irapeanum, Habenaria spathacea, and Corallorhiza meocicana flourish in 

 the shade of the oak-forests, while Spiranthes aurantiaca, S. saccata, S. violacea, and 

 Bletia coccinea affect the savanas, half concealed among such grasses as Manisurus 

 granulans, Elionurus ciliaris, Andropogon anthistirioides, Panicum sylvaticum, &c. 



The neighbourhood of Jalapa (Coatepec, Jilotepec, Zacuapan, Sec.) and Orizaba, and 

 the greater part of the magnificent country stretching along the eastern side of the 

 cordillera of Oaxaca and bearing the name of Chinantla, belong to this subregion, the 

 extensive savanas of which are characterized by Malpighiacese, Mimoseae, Escobedia 

 IcBvis, &c. Here the soil is usually arid, though the rains are frequent, but here and 

 there groups of taller trees relieve the monotony of the vast expanses. 



Second Subregion : Temperate, or Begion of Tree-ferns. — This is the region which in 



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