GEOGRAPHICAL BOTANY. 395 



the limits of the plants, cannot be satisfactorily deter- 

 mined. In the following sketch of Galeotti's regions, 

 the local displacements are added within brackets to the 

 altitudes given. 



1. Hot regions. 0' 3000' (25000. Vegetation from 

 December to May (end of October to June) languid : 

 most of the trees leafless. 



a. Eastern coast with forests of Rhizophoras. Mean 

 temperature = 95 c. 



b. Moist mixed forests, not, however, containing many 

 Ferns (R. chaude temperee des ravins). Mean tempe- 

 rature, 25 19 c. 



c. Coast forest of the Pacific, 25 19. 



2. Temperate regions. 



a. Eastern slope. 3000 6000' (5500', 70000. This 

 region differs from the coast in its great humidity and 

 evergreen foliage. It contains tree-ferns, Liquid-ambar, 

 evergreen oaks (a feuilles luisantes), and numerous Orchi- 

 daceae. Mean temperature = 19 to 15. In Oaxaca, 

 this region is less distinctly separated from the others : 

 the pine trees here descend as low as 3000', whilst Myr- 

 taceae, Melastoma ( , &c., are found even at an elevation 

 of 7000'. The soil is calcareous, and Galeotti found 

 there only 21 Ferns, whilst on the volcanic soil of Vera 

 Cruz, he found 77 species at the same level. 



b. Western slope. 3000' (10000 to 6500'. Mean 

 temperature = 20 to 15. To it a large part of Oaxaca, 

 of Mechoracan, and Xalisco belong. Tree-ferns are not 

 found there, and in fact few Ferns, but a large number 

 of oaks, with numerous Orchidacese growing parasitically 

 upon the bark, and some Palms. 



c. Plateau, and the slopes adjacent to it, mean tem- 

 perature = 2 0to 15 (21tol8). The internal slopes of 

 Mexico differ in every case, botanically speaking, from 

 those situated externally, and inclined towards the two 

 oceans. Their dry climate, for the most part, excludes 

 the vegetation of Ferns and Orchidacese. These elevated 

 surfaces are characterised by the large number of Cacti : 



