454 
WRIGHT : FOLIAR PERIODICITY 
of temperature as a factor influencing the development of 
tropical forests is less significant than that of the hygrométrie 
conditions of the air. 
In this part of the paper we are concerned with the possible 
effect of a high temperature or variation of temperature on 
the fall of old leaves and the production of new ones. 
To determine the effect of a difference in temperature alone 
it would be necessary to select districts where the rainfall, 
humidity, and climatic periodicities were the same—an 
agreement which it is impossible to find in any part of Ceylon. 
Colombo and Hakgala are approximately similar to Pera- 
deniya as regards annual rainfall and climatic periodicity, 
but the humidity at Hakgala is much higher than at either 
place, and our comparison is therefore confined to Colombo 
and Peradeniya. At Colombo the humidity is one degree 
higher and the rainfall about six inches greater than at Pera¬ 
deniya. The temperature is 5° F. higher at Colombo than at 
Peradeniya. The higher temperature in the Colombo district 
is not accompanied by a notable increase in the number of 
deciduous species. The differences in temperature alone in 
parts of Ceylon appear to have very little, if any, effect on the 
phenomenon of defoliation. It is true that at Hakgala and 
other places at high altitudes the temperature is 15° F. lower 
than at Peradeniya, and the vegetation is almost evergreen ; 
but it is equally true that at Mannar with a temperature more 
than 6° F. higher than at Peradeniya there is not a propor¬ 
tionate increase in the number of deciduous species. A slight 
increase in the deciduous species may be met with in the 
inland hot northern parts of Ceylon, but it can usually be 
ascribed more to the poor rainfall and low humidity rather 
than to the high temperature. Disregarding differences of 
climate, there occurs in Ceylon a decrease in the number of 
deciduous species with a fall in temperature, and equality or 
slight increase with a rise of temperature. In passing from 
the tropics to the temperate zones there is an increase in the 
percentage number of deciduous trees with a decrease in 
temperature. 
