Ch. IV] WARM TEMPERATE MOIST SUMMER DISTRICTS 493 



(Fig. 257). The already-mentioned Aspidosperma Quebracho, species of 

 Celtis, Anacardiaceae (Fig. 258), Zygophyllaceae, are also common. As 

 in the thorn-woodland of the tropics, so here also pinnate leaves prevail 

 (Leguminosae, Zygophyllaceae, Anacardiaceae). Aphyllous plants are 

 common among the shrubs. Richness in ethereal oils is characteristic of 

 man)' species, in particular of Terebinthinae. 



Fig. 256. Prosopis alba, Griseb. A tree of the Argentine thorn-forest (espinal-formation). 

 Half natural size. After Hieronym us. 



Completing the picture of a thorn -forest quite tropical in appearance are 

 crowds of climbing plants, chiefly herbaceous (Bignoniaceae, Asclepiadaceae, 

 Convolvulaceae, Cucurbitaceae), many Opuntiae, and in the most desert- 

 like districts also species of Cereus as tall as pillars, markedly xerophilous 

 large Tillandsiae, together with various Loranthaceae on the branches of the 

 trees, and a meagre vegetation of stiff grasses and small-leaved Compositae 

 springing from the usually hard bare soil 1 . 



Similar thorn-bushland may occur in Mexico, and it appears also to be 

 formed in South Africa. 



ii. SAVANNAH-FOREST. 



An essentially different picture and one much more attractive than that 

 of the thorn-forest is afforded by the savannah-forest, which occurs in 



1 See regarding these forests, Lorentz, op. cit., p. 20; Tschudi, op. cit., p. 14. 



