.346 



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 vioiisooii-forcsts'^. 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 bj- grass- 

 land, usually of the 

 savannah type. Still 

 greaterdrought induces 

 the desert character. 

 Tropical desert will 

 be discussed in con- 

 nexion with temperate 

 desert ". 



The oecologicai 

 physiognomy of vege- 

 tation in periodically 

 dr)' 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 anc 

 show .xerophilous vege 

 tation at all seasons o 

 the year. Here thi 

 danger of desiccation 

 especially threatening 

 to tall plants, has lee 

 to the evolution o 

 YnghXy xe7-op/iiloiis treei 



Fig. 1S4. Bombax malab.iricum in the dry season bearing Iriiil. 

 Ceylon, from a photograpli. 



treei 

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

 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 analogue; 

 m Central Europe and first appear, in a feebly defined form, in thi 

 Mediterranean region. 



' See p. 260. -^ See p. 616. 



