458 
WRIGHT : FOLIAR PERIODICITY 
(5) Atmospheric Humidity. 
The humidity of the air is probably one of the most 
important factors in the defoliation of trees in the tropics. 
It can be shown by comparing Peradeniya, Hakgala, 
Colombo, Badulla, and Mannar, that the maximum yearly 
humidity obtains at Hakgala where the vegetation is 
more nearly evergreen than at any of the other places, and* 
that the minimum humidity is at Peradeniya where the 
vegetation is perhaps more deciduous than in any of the places 
mentioned. The high humidity at Mannar—four degrees 
higher than at Peradeniya—is probably responsible for the 
stunted and often succulent nature of the vegetation and 
for the non-increase in the number of deciduous species 
compared with Peradeniya. 
It is important to notice that the Peradeniya, Hakgala, 
Colombo, and Badulla districts, which represent different 
climates, ranging from sea level, to over five thousand feet 
above sea level show a definite relationship between a 
particular stage of humidity and defoliation. In all these 
districts it is only when the humidity falls near to or below 
70 degrees that the majority oi the deciduous species drop 
their leaves. 
The best agreement is, however, between the varying 
humidity and number of deciduous trees at a given place 
throughout the year. In each of the districts mentioned 
the number of deciduous species increases with increased 
dryness of the air and decreases with an increase in the 
dampness of the air If the curves showing the relation- 
shtp between hunudity and number of deciduous species 
at Peradeniya are examined it will be seen that the 
“f “f* 7 “ < T rieDced “ February and March, 
“tenths when the maximum percentage 
TaC' vrrz r ies drop their ,aa ™«^ 
fr J t P , May ’ When the temperature is higher 
“ 0 lM8e : ‘r ^ ” 0t ** actuany 
decreases on account of an increase in the dampness or 
