460 
WRIGHT : FOLIAR PERIODICITY 
A glance at the curve indicating the number of species 
which are leafless or undergoingdefoliationduring each month 
shows that in February when the rainfall and humidity are at 
the minimum the defoliation of the species is most active, 
and the same conclusion holds good for the dry month 
of March. But in April the rainfall and humidity of the 
air increase considerably, and though the temperature is 
higher than in February or March, the number of trees under¬ 
going their leaf change is considerably reduced. Equally 
striking is the fact that from June to October the humidity 
is near the maximum, the rainfall is abundant, and the 
defoliation of the deciduous trees is at the minimum. A 
better or more complete comparison could not be desired to 
prove that in a climate like that at Peradeniya there is an 
increase in the defoliation or leafless stage of deciduous species 
during the dry period and a decrease during the hot moist or 
relatively cool and moist periods. 
In other parts of the island such as Nuwara Eliya and 
Hakgala there is a coincidence between high humidity and 
heavy rainfall and the prevalence of a more or less evergreen 
vegetation. At Mannar a low rainfall and high atmospheric 
humidity prevail, and there is an approximate similarity in 
the number of deciduous species to that at Peradeniya- 
Such facts indicate the importance of humidity in connec¬ 
tion with defoliation in the tropics. 
From considerations of the humidity, rainfall, temperature, 
and foliar periodicity in Buitenzorg, East Java, and parts of 
Ceylon, it may be concluded that (1) a high temperature is of 
the minimum importance, and (2) low humidity and scanty 
rainfall are clearly associated with leaf-fall. Where the 
humidity and rainfall are more or less constant throughout 
the year there is less agreement between the time of foliar 
activities ; where there is a wide variation in these factors 
throughout the year there is a more marked leaf-fall at the 
driest time of the year. 
