348 



ZONES AND REGIONS 



[Pt. Ill, Sect. I 



that such protection is required in the open savannah country as well as on 

 high mountains. The same is true of the trees with their branches in tiers, 

 such as Terminalia Catappa, Bombax malabaricum, which I have seen 

 likewise only in open situations and in well-lighted bush. Much is to be 

 said for the view, which Reiche has already put forward, that the umbrella- 



FiG. 185. Acacia of umbrella-form. From the East African savannah. After Engler. 



forms have arisen as a means of protection against the wind, but 

 experiments alone can decide the question. 



Xerophilous trees of the tropics are mostly bare during dry weather ; 

 their foliage, although present only during the rainy season, is usually firm 

 and provided with elaborate protective devices against transpiration. 

 Pinnate leaves are specially frequent, and by their mobility, which permits 

 them to assume the best position for the time being, they are thoroughly 



