IN CEYLON. 
445 
nearly all of the same size and age, and the difference in 
their periodicities during a given year points to the import¬ 
ance of the individual requirements of each tree and the 
relative insignificance of external or climatic forces in 
connection with foliar periodicity. 
5.—Transpiration in OeyBon and the Tropics 
generaily. 
The production of new leaves is closely associated with 
root activity and the transpiration of water from the leaves. 
The phenomenon of defoliation at regular intervals is 
similarly related, and for a proper understanding of foliar 
periodicity in Ceylon and the tropics generally it is necessary 
to consider the subject of transpiration in such regions. In 
temperate zones the deciduous trees lose most water by 
transpiration from the young spring leaves, or during the 
summer months when the full complement of foliage is 
exposed to a relatively hot and dry atmosphere ; in autumn 
the loss by transpiration is reduced, and during winter the 
trees are leafless. 
From the foregoing remarks it is obvious that in tropical 
areas there is no period exactly analogous to a temperate zone 
winter. In many parts of the tropics the conditions allow 
of transpiration throughout the greater part of the year, and 
in other areas short periods of dry weather may intervene. 
The available literature dealing with this aspect of the sub¬ 
ject is somewhat scanty, and the following remarks are 
mainly in reference to observations made in Ceylon. 
The transpiration of plants is influenced by the tempera¬ 
ture and humidity of the air. In the tropics the temperature 
is usually high and the humidity high or low. Where the 
temperature and humidity are uniformly high, the vegetation 
is rarely xerophytic, as is evidenced in parts of Ceylon and 
Buitenzorg in Java. If however the temperature is high 
and the rainfall meagre, the plants become spiny or succulent 
and the xerophytic type of vegetation 'may predominate ; 
8(9)05 J (12) 
