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WRIGHT : FOLIAR PERIODICITY 
dealing with the leafless phase and the importance of the 
climatic factors. 
In a tropical district like Peradeniya the foliar periodicity 
may be determined by internal and external factors, and 
each species must be considered separately. The more 
equable the climate in different parts of Ceylon the more 
conspicuously will the internal forces operate, and the 
more independent they will be of climatic influences. My 
statement at the British Association Meeting of 1902 that 
botanists desirous of studying the internal forces in plant 
life should select a tropical country other than Ceylon is 
still supported by the further results of this investigation. 
In a general way it maybe said that the nearer to the tropics 
the more the personal equation influences the phenomena 
of plant life, and as we pass from the equator—north or 
south—the less the power of the internal forces and greater 
the power of climate in determining the periodicity of 
plant life. 
Even in those parts of the tropics where there are definite 
seasons, the phenomena appear to be the outcome of climatic 
and individual forces. In more equable tropical zones, with 
the minimum climatic variation, the plant phenomena are 
almost entirely determined by the individual requirements. 
Respecting the effect of internal and external factors the 
main points may be summarized as follows :— 
(1) The foliar periodicity of deciduous trees is inherent in 
tropical and temperate zones since it is observable in all these 
areas. 
(2) The more equable and tropical the climatic conditions 
the larger is the number of arborescent species and the 
larger is the proportion of the evergreen trees in the flora. 
(Of. British and Ceylon tree flora.) 
(8) The more marked the climatic periodicity the less the 
internal forces are obvious and the more evident are the 
external forces. At Buitenzorg, where the climate is 
relatively equable throughout the year, the power of the 
