CHAPTER II 



THE PERIODIC PHENOMENA OF VEGETATION 

 WITHIN THE TROPICS 



i. General Prevalence of Periodic Phenomena in the Functions of Plants. No 



absolute period of rest. Rest only for some processes. Occurrence of periodicity in 

 tropical vegetation. 2. Periodicity in the Vegetative Domain, i. Leaf-fall. Frequency 

 of periodic leaf-fall within the tropics. Diversity in appearance of trees during the dry 

 seasons. Seasons of the year and vegetation in the campos. ii. Growth. Periodic 

 defoliation in certain species independently of the season. Individual periodicity of the 

 separate shoots of many tropical plants, iii. Temperate Woody Plants in the Tropics. 

 3. Periodicity in the Sexual Domain, i. General Considerations. Separation in 

 point of time of vegetative and reproductive activity, ii. Constantly Humid Districts. 

 Non-contemporaneous flowering of different twigs in woody plants. Simultaneous flower- 

 ing of all individuals of a species without relation to the season of the year. Connexion 

 between formation of flowers and leaf-fall. iii. Periodically Dry Districts. Abundance 

 of flowers in the dry seasons and at the commencement of the wet seasons. Poverty in 

 flowers at the height of the wet season. The wet season the period for ripening fruit, 

 iv. Special Cases. Climate and flowering season in Java, in North-west India, in Ceylon, 

 in British Guiana. 4. The Caesalpiniaceae in the Botanic Garden at Buitenzorg. 



i. GENERAL PREVALENCE OF PERIODIC PHENOMENA 

 IN THE FUNCTIONS OF PLANTS. 



The periodic phenomena of tropical vegetation have hitherto been 

 investigated only to a slight extent. As a result of the scanty and usually 

 incorrect data supplied by travellers, the notion has been pretty generally 

 disseminated that in constantly humid tropical districts vegetative and repro- 

 ductive activity proceeds without interruption, whilst the well-defined dry 

 seasons of other districts cause their vegetation to undergo periods of rest. 



Observations in tropical districts with abundance of rain at all seasons 

 of the year have taught me that there also vital processes in plants exJiibit 

 a rhythmic alternation of periods of repose and of activity. This opinion, 

 however, depends on a conception of periods of rest that differs from the 

 usual one. 



The more recent investigations, especially those of Sachs and Muller- 

 Thurgau, have proved satisfactorily that there are no periods of rest for the 



