434 
WRIGHT : FOLIAR PERIODICITY 
Peradeniya—there is a rythmical change of periods of rest 
and activity. It can also be shown that the observed 
variability of certain species in different climates is repeated 
when individuals of these species are grown in the same 
climate or individually from year to year. It is by a con¬ 
sideration of such observations that one is led to infer 
that foliar periodicity is inherent and that in many tropical 
areas the internal factors are responsible for many phases of 
the vegetation. 
On the other hand, these facts also teach us that the climatic 
periodicity in parts of Ceylon and Java is so marked as to 
influence the foliar activities. The inherent periodicity in 
foliar production can be affected by external climatic forces 
such as obtain in these places. 
Variation of a Species in different Climates . 
It is a matter of common knowledge that the same species 
grown in different climates or changed environments 
presents many differences. We have seen that in various 
parts of Ceylon different climates exist, and a discussion of 
the variation of plants of the same species in such localities 
can be conveniently introduced in this part of the paper. 
The variation in foliar periodicity due to a difference of 
climate in Ceylon is usually one of time only, and in very 
few cases can it be shown that plants of the same species may 
be evergreen or markedly deciduous according to the climate 
in which they are growing. There are three species which 
though evergreen in the Peradeniya and wet districts in 
Ceylon, are partially deciduous in the dry Mannar Districts, 
these being Thespesia populnea, Sol.; Diospyros ovalifolia, 
R« Wight, and Diospyros montana, Roxb. This statement 
is only intended to apply to parts of Ceylon, and does not 
hold good when species common to Ceylon are introduced 
into other countries. 
It will be necessary, in order to avoid confusion, to first 
consider the variation of a species in parts of Ceylon and 
