(HAP. V] TROPICAL DISTRICTS WITH DRY SEASONS 359 



are termed ' mj'ombo,' are dominant and sometimes pure ; thus in Unyamwezi Berlinia 

 Eniinii occurs, but species of Acacia, Sterculia, Terminalia, and Kigclia also occur. 

 There is little underwood, the shrubs and small trees of Anona, Combretum, and 

 others are so scattered that travelling through the myombo-forests is in no way 

 impeded. Succulent plants are rare, only here and there is an Aloe or a can- 

 delabra-like Euphorbia ; but numerous herbs cover the ground '.' 



iv. TROPOPHILOUS AND XEROPHILOUS WOODLAND IN 

 TROPICAL AMERICA. 



The high forest of the interior of South America, especially of Brazil 

 south of the Amazon, is in part tropophilous and should be classed as 

 monsoon-forest. The forests of Minas Geraes described by Warming 

 slied their foliage periodicalh', but without ever becoming leafless, as the 

 defoliation of most of the trees immediately precedes their acquisition of 

 new foliage. 



The marked xerophilous types of savannah- forest and thorn- forest 

 (including thorn-bush) are richly represented throughout the whole of 

 tropical America, and frequently alternate with savannah. Wherever the 

 humidity increases the savannah first passes over into savannah-forest. 

 So at least I have observed in Venezuela, where on climbing the coast 

 Cordilleras from the south the hitherto scattered trees closed in to form 

 an almost close forest, the soil retaining its grassy growth. The low forest, 

 comparable with a dense orchard, consisted chiefly of Leguminosae with 

 umbrella-shaped crowns, especially of species of Cassia, whose completely 

 defoliated twigs were decked with yellow flowers. Scattered among the 

 leafless trees appeared two evergreen, very thick-leaved species of trees, 

 Rhopala complicata (Proteaceae) and the caju, Anacardium occidentale. 

 All the branches, especially those of the leafless trees, bore small hard- 

 leaved or densely hairy species of Tillandsia, among which T. recurvata 

 was very abundant, and also a few markedly xerophilous orchids, in par- 

 ticular a beautiful flowered species of Jonopsis. Amongst the trees a 

 columnar species of Cereus, equal to them in height, was frequently noticed. 

 The soil was covered with rich and tall but completely dried-up grass. 



Savannah-forest certainly occurs also in other parts of tropical America. 

 Thus, apparently belonging to this type, there are ' capoes,' forest-tracts 

 replacing the vegetation of the savannah (campos) on moister ground in 

 Central Brazil (see Fig. 127). 



Thorii-woodlaiid, as forest, bush, or shrub, is extensively developed \\\ 

 tropical America. It forms an essential part of the coast vegetation in 

 East Central Mexico (Fig. 12S). Under the well-known and dreaded 

 name of ' caatinga,' in particular it covers extensive tracts of country with 

 a small rainfall in Brazil, between the savannahs icampos) of the south 



' Engler, op. cit., p. 62. 



