IN CEYLON. 
477 
growth, and therefore the production of homogeneous secon¬ 
dary xylem. For in addition to the existence of about two 
hundred deciduous trees now growing in Ceylon one must 
acknowledge that there are regular periodicities in a 
large number of evergreen plants, in many of which the 
phenomenon is inherent and may lead to the production of 
a heterogeneous wood. The observations tabulated in this 
paper prove that foliar and other activities may be periodic 
in equable or tropical regions, that many plants pass through 
a leafless phase at any time of the year in a district like 
Peradeniya, and that the foliar periodicity exhibited may 
or may not lead to differentiations in the secondary xylem. 
It will be shown in a later paper that in the tropics many 
deciduous trees do not show rings of growth, and further 
that quick-growing evergreens may show them. The results 
prove (1) that the differentiation of rings of growth 
in the stem is not.confined to deciduous specieB; (2) that 
the foliar periodicity of trees is not necessarily due to 
the existence of a climatic periodicity ; and (3) that rings 
of growth are not, in ail cases, determined by foliar 
periodicities, neither are they a guarantee of the existence 
of a climatic periodicity. Such phenomena may be an 
expression of the autonomy of the plants dealt with, and one 
cannot be too cautious when considering the value of rings 
of growth as indicators of past climatic conditions. The 
subject of xylem differentiations is excluded from the present 
paper, but it is so closely associated with the foliar activity of 
trees in the tropics during our hot dry, hot moist, and dull 
wet months that the paper would have been incomplete 
without some reference to this subject. 
11.—The Foliar Periodicity of Ceylon Endemics. 
The endemic trees of Ceylon comprise no less than 274 
species, or a little less than half the total number of arbores¬ 
cent species native to the Island. The foliar periodicity of 
the endemic plants is of great importance, as it shows the 
behaviour of plants which are known in Ceylon only, and 
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