34^ 



ZONES AND REGIONS [Pt. Ill, Sect. I 



season and renew it at or immediately before the commencement of the 

 monsoon-rains ; apart from this they have only xerophilous organs well 

 protected against drought. Such tropophilous forests, whose alternating 

 hygrophilous and xerophilous character is regulated by the monsoon, have 

 been termed monsoon-forests l . Regions with less abundant rainfall are, 

 according to the character of their climate, occupied by xerophilous wood- 

 land (savannah-forest, 

 thorn-forest, thorn- 

 bushland) or by grass- 

 land, usually of the 

 savannah type. Still 

 greater drought induces 

 the desert character. 

 Tropical desert will 

 be discussed in con- 

 nexion with temperate 

 desert 2 . 



The oecologicai 

 physiognomy of vege- 

 tation in periodically 

 dry districts is quite 

 different from that in 

 constantly humid ones, 

 especially if we con- 

 trast with humid dis- 

 tricts those districts 

 which, above all, have 

 a scanty rainfall and 

 show xerophilous vege- 

 tation at all seasons of 

 the year. Here the 

 danger of desiccation, 

 especially threatening 

 to tall plants, has led 

 to the evolution of 

 highly x crop J i ilons trees, 

 forming an extremely peculiar tree-type which, in particular, shows its 

 characteristic features in savannah and thorn-forest. 



Investigations are greatly needed in regard to the structure and con- 

 ditions of existence of tropical xerophilous trees, which find no analogues 

 in Central Europe and first appear, in a feebly defined form, in the 

 Mediterranean region. 



1 See p. 260. 2 See p. 616. 



FlG. 184. Bombax malabaricum in the dry season bearing fruit. 

 Ceylon. From a photograph. 



