IN CEYLON. 
417 
foliar renewal with the periodical change of seasons in such 
areas, but quotes many instances which indicate that in tropi¬ 
cal districts internal factors can be recognized. Schimper* 
and Ursprung! also dwell upon the tendency to interpret 
the phenomena in the tropics in terms of our knowledge of 
temperate zone plants. 
It is one of the objects of this paper to prove that generali¬ 
zations respecting foliar periodicities and their significance 
should not be made until a study of plants has been carried 
out in tropical areas where the physical conditions are 
compatible with a display of the autonomy of the plants. In 
temperate zones the vegetation only shows outward signs of 
life in spring and summer, whereas in the tropics conditions 
may exist for a perpetual display of activity on the part of 
one or more functions of the plants. 
It need only be pointed out that there is not a month in 
the year, at Peradeniya, when all the plants are in full 
possession of their leaves ; that some plants may produce a 
complete set of new leaves once or twice each year, others a 
complete and several sets each year, and others every month 
in the year, to convince anyone of the necessity of formu¬ 
lating plant-laws only after considering the vegetation in 
tropical areas. 
The influence of temperature alone, suggested as being of 
importance by Sachs, Schimper, and many others, has been 
shown to be of minor importance in affecting the phenomena 
of leaf-fall and renewal in Ceylon. It is only in parts of 
the tropics where there is a minimum climatic periodicity 
and minimum variation in humidity and rainfall that the 
influence of temperature alone can be thoroughly worked 
out. If one attempts to work out the influence of tem¬ 
perature on the various functions of plants in a temperate 
zone he is necessarily handicapped, since he is dealing with 
* Pflanzen-Geographie auf physiologischer Grundlage ; Dr. Schimper, 
1898. 
t Anatomie und Jahresringbildung Tropischer Holzarten ; Alfred 
Ursprung, 1900. 
