IN CEYLON. 
473 
transpiration current will most probably have an appreciable 
effect on the metabolism within the parenchymatous 
elements. The question of division of labour is also one 
which may be considered. During the resting period many 
changes already mentioned by Schimper are taking place. 
These changes are necessary and may be required to be 
effected before foliage is renewed in order to avoid stagnation 
or general interruption. During the beginning and early 
period of the leafless phase the cambium is comparatively 
inactive, and the growth which takes place will therefore 
consist more in the thickening of the walls and general 
strengthening of the existing elements than in the produc¬ 
tion of new cells. During the end of the period of defoliation 
there is usually formed a series of closely set thick-walled 
elements which contrast sharply with those formed when 
the new leaves are produced. 
The above are a few of the possible advantages which 
may be associated with the foliar phenomena in the 
tropics, but it must be remembered that no matter how 
significant the advantages may be, they have not, in Ceylon, 
resulted in a wide distribution or persistence of a large 
number of deciduous species. The evergreen trees, which 
do not show periodic foliar phenomena in the sense that 
the deciduous trees do, but maintain a more or less regular 
rate of leaf, flower, and root activity throughout the year, 
comprise the greater part of the tree flora of this Island. 
9-- Relation off Fofiaar, Floral, and Fruit 
Periodicities. 
With most Ceylon evergreens the production of flowers is 
usually subsequent to that of new leaves. It is not possible, 
owing to insufficient information, to describe the relationship 
between flower and leaf production in all our deciduous 
species, but if one tabulates the observed results certain 
definite cycles are found to be characteristic of known species. 
Out of twenty-one recorded species it is interesting to find 
that in eight of them, viz., Careya arborea, Sterculia 
