252 ZONES AND REGIONS [Pt. Ill, Sect. I 



the leaves were still small and pale, but on the sterile ones they were 

 already large and bright green. On December 13, after the flowering 

 period, the tree that had flowered abundantly could be easily distinguished 

 from the other by its less developed foliage. In Meliosma lanceolata, in 

 the same garden, on November 21, I saw young foliage only on sterile 

 boughs, whilst the twigs provided with infructescences or young inflor- 

 escences still showed no signs of foliage. 



Many trees in their youth, so long as they do not produce fiozvers, are 

 evergreen, tvhilst later on they shed their leaves before the impending 

 blossoming period. This is the case, for instance, with Schizolobium gigan- 

 teum, at least in Java. 



It is evident from the foregoing remarks that, like leaf-formation and 

 leaf-fall, the development of flowers depends on a periodically recurring 

 internal condition of the plant. Shoots that flower continuously no more 

 exist than do those that are continuously forming foliage. /;/ the repro- 

 ductive domain, then, there occurs a rhythmic alternation of rest and activity 

 depending on internal causes. 



iii. PERIODICALLY DRY DISTRICTS. 



The rhythm that is witnessed in leaf-formation is observable also in 

 the flower. The production of floivers exhibits a correlation with the 

 seasons of the year, whenever the seasons display sharply defined differences. 

 In the reproductive domain this dependence is likewise a secondary 

 feature — an adaptation to external factors on the part of physiologically 

 necessary processes. In the tropics an influence associated with variations 

 in temperature is exhibited only in border-districts, and consequently need 

 not be considered here. Over the greater part of the torrid zone, the 

 difference in the seasons, as far as these concern plant-life, is expressed 

 only in the atmospheric precipitations, and in particular in the rainfall and 

 the atmospheric humidity. 



The blossoming of zvoody and tuberous plants everyivhere within the tropics 

 is most abundant during the dry season, or immediately after it ; and these 

 are precisely plants in which the production of flowers is not directly 

 dependent on the foliage. We frequently find it stated in the accounts 

 of travellers, as a remarkable phenomenon, that many trees blossom 

 precisely in the dry season. Belt makes this statement concerning 

 Nicaragua, Criiger concerning Trinidad, Schweinfurth concerning Nubia, 

 and Kurz says of the deciduous forests in Pegu, that most of the trees 

 blossom during the hot dry season, that a number of plants with rhizomes 

 and tubers — for instance, Scitamineae, Amaryllidaceae, Orchidaceae, Ochna 

 suffruticosa — at the same time burst into blossom, and finally that the 

 leafless dried branches of the trees are covered with flowering orchids. 



I became personally acquainted with the abundance of blossom during 



