IN CEYLON. 453 
6.—The relative importance off the physical factors: 
temperature, humidity, rainffall, and light. 
It has been shown that the climatic changes at Peradeniya 
are coincident with periodical foliar phenomena, and that 
when the atmospheric humidity is lowandthe rainfall scanty, 
there is a large increase in the number of trees which drop 
their leaves and remain leafless for varying periods of time. 
It is now necessary to deal analytically with the separate 
factors, and if possible to determine the relative significance 
of a variation of temperature, humidity, rainfall, and light on 
the foliar periodicities of plants in Ceylon. The factors, 
when acting together in different intensities, have been 
shown to produce an effect on the time of defoliation, in the 
section dealing with the influence of climate. The power 
of each factor can be considered in regard to the effect on 
the manner and time of defoliation and also on the number 
of deciduous species. 
Temperature. 
The high temperature in the tropics so forcibly impresses 
the ordinary visitor that he naturally expects that its influ¬ 
ence on plant growth and therefore foliar periodicity will be 
considerable. Sachs, when speaking of vegetative activity 
and rest, suggested that the periodicity may chiefly depend 
upon temperature and moisture. He stated that in any one 
species, each vegetative phenomenon possessed its cardinal 
points of temperature, and when dealing with deciduous 
trees in temperate zones he asserted that it was mainly the 
lower temperature of winter which led to defoliation, and 
the rise in temperature in spring which made it possible for 
the shoots to burst into new leaf. 
Vines states that for any given degree of temperature 
there is a corresponding rate of growth. 
pfeffer points out that in certain cases the growth of leaves 
is unaffected by variations of temperature. 
Schimper, after describing the high temperature and 
luxuriant vegetation in the tropics, stated that the importance 
8(9)05 (13) 
