Chai\ V] TROPICAL DISTRICTS WITH DRY SEASONS 349 



in harmony with the climatic conditions. Evergreen trees, on the other 

 hand, usually have simple, often very hairy, leaves, which in many cases 

 contain so much silica that they assume a consistency resembling sheet- 

 metal, and, in the wind, rattle with a metallic sound, as in the proteaceous 

 Rhopala complicata, a characteristic tree of the llanos. The foliage-buds 

 are provided with a coating of protective scales as thick as, or even thicker 

 than, that of trees of the temperate zones (Fig. 186). Only the flowers 



Fig. 186. Xerophilous foliage-buds. From the Brazilian campos. Left hand : Myrcia longipes. 

 Centre : Eugenia Jaboticaba. Right hand : Eugenia dysenterica. After Warming. 



apparently dispense with a corresponding protection, and even frequently 

 possess large delicate corollas, although they often open at the height of 

 the dry season, and therefore demand large quantities of water for trans- 

 piration. 



The volume of the wood in comparison with that of the foliage is greater 

 than in hygrophilous trees, and the cortex 

 is frequently covered by a massive scaly 

 bark (Fig. 187). 



Besides the protective devices against 

 drought that have been mentioned, and 

 which occur and are similarly differen- 

 tiated in xerophytes of higher latitudes, 

 there are among the tropical woody plants 

 cases of special and very peculiar adapta- 

 tion. Thus many tropical trees owe the 

 faculty not only of growing in very dry 

 regions, but also of attaining large and 

 even gigantic dimensions, to the fact that 

 they store up large supplies of water for 

 the dry season. Amongst these trees is 



the mighty baobab (Adansonia digitata) of the African savannah, which 

 will be dealt with subsequently ; in addition the wonderful bottle-trees 

 (Cavanillesia arborea (Willd.), K. Schum., and other Bombaceae) of the open 

 thorn-bush of Central Brazil, the trunks of which, swollen like a cask up to 

 a thickness of five meters (Fig. 193), serve as water-reservoirs ; also, in the 

 same forests, Spondias tuberosa (Anacardiaceae), the tuberous swellings 

 of whose roots become filled with water. Finally, in contrast with rain- 



Fig. 1S7. Sweetia dasycarpa. From 

 the Brazilian campos. Transverse section 

 through the stem. After Warming. 



