348 



ZONES AND REGIONS 



[Pt. Ill, Sect. I 



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

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

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

 likewise onl}- 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- 



FlG. 185. Acacia of umbrella-form. From the East African savannah. .-Vfter Engler. 



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

 experim.ents 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 firn:! 

 and provided with elaborate protective devices against transpirationj 

 Pinnate leaves are specially frequent, and by their mobility, which permit-j 

 them to assume the best position for the time being, they are thoroughl>| 



