35° 



ZONES AND REGIONS 



[Pt. Ill, Sect. I 



forest and monsoon-forest, xerophilous woodland, especially in the thorn- 

 forest, contains arborescent succulents, particularly species of Cereus in 

 tropical America (Fig. 128), and of Euphorbia (Fig. 198) in Africa. 



The shrubs of the savannah are not less xerophilous than the trees. 

 Their hypogeous parts are very strongly developed as compared with 

 their epigeous parts, and often form such a massive system of thick 

 lignified axes that, following Lund and Liais, we may describe some of 

 them, such as those of Andira laurifolia and Anacardium humile of the 

 campos, as hypogeous trees. In Andira, for instance (Fig. 188), the 

 system of rhizomes, consisting of branches as thick as one's arm, frequently 



Fig. 188. Andira laurifolia. From the Brazilian campos. After Warming 



covers an area ten meters in diameter, whereas the epigeous foliage-shoots 

 are thin and never more than a meter in height. Such hypogeous 

 axes appear to serve as water-reservoirs, as also do the tuberous woody 

 rhizomes that occur on numerous small shrubs and bushes in the campos 

 (Figs. 203, 204). 



Thin woody lianes occur in xerophilous woodland, in particular in 

 thorn-forest, but disappear in the savannah ; but in the savannah, for 

 instance in the Brazilian campos, there are found erect shrubs belonging 

 to families and genera that with these exceptions include only climbing 

 forms. Schenck considers it probable that many of these shrubs have 

 been derived from lianes and are to be considered as cases of reversion to 



