CiiAi'. II] PERIODIC PHENOMENA IN THE TROPICS 243 



humid districts is an illusion. To the attentive observer repose is manifest 

 ;ver)'\vhere side by side with activity, and both these conditions continually 

 nterchange like the parts of a kaleidoscope. The difference between such 

 1 vegetation and one exposed to the influence of alternately favourable and 

 anfavourable seasons is confined to the f;act, that in the constantly humid 

 district the sum of repose and activity remains approximately constant in 

 very season, whilst in districts with alternating seasons it periodicall)' 

 ncrcases and decreases. 



2. PERIODICITY IN THE VEGETATIVE DOMAIN, 

 i. LEAF-FALL. 



In spite of numerous travellers' reports to the contrary, the notion still 

 )revails that tropical forests are for the most part evergreen, and essentially 

 )ccupy constantly' moist districts onl)', whereas districts with markedly dry 

 easons are supposed to produce forest growth only along the margins 

 f water-courses. This incorrect idea is connected with the no less 

 ncorrect assumption that dry seasons are unsuitable for forests. 



In reality the case has quite a different aspect. TIic tropical forest is for 

 he most part composed of periodically leafless trees, and. as has already been 

 hown \ is b}' no means excluded from districts with very dr}' and hot 

 easons. Indian forest-botanists, especially Brandis and Kurz, were the 

 rst to make us acquainted with the distinctive characters of tropical 

 Drests that are evergreen and forests that are green in the rainy season. 

 Voodland in districts with periodic and well-marked dry seasons has 

 uring the dry season a greater resemblance to Central European woodland 

 uring winter than to the dense luxuriant rain-forests which are usuallj' 

 ;garded as the typical tropical forests. The picture of repose, however, 

 hat is evoked by the dry season, is much less uniform than that of a winter 

 indscape in temperate zones. 



Thus, in many cases, woodlands near the water retain all their foliage or 



large part of it during the dry season, and form green strips and spots 

 n the landscape which is otherwise mainly brown and grey in tint. In 

 ddition, outside the reach of water-infiltration, differences in the chemical 

 nd physical nature of the soil affect the time and extent of the leaf-fall. 

 i^ greater amount of moisture in the soil delays defoliation and accelerates 

 iie opening of the leaf-buds. Warming has also observed that woody 

 lants growing on a calcareous soil become barer of foliage than on other 

 inds of soil. 



Specific differences in woody plants also come into play. Under identical 



' See p. 165. 

 R 2 



