THE AMERICAN BOTANIST. 



95 



conditions which are physically identical, yet the time of 

 fall of old leaf, production of new leaf and of flowers differs 

 considerably in specimens of the same species. In the first 

 mentioned species, the variation is a question of months, 

 and to see members on the same plot, dropping their 

 leaves when others are quite bare, others in full old leaf, 

 and others in full new leaf and flower impresses one with 

 the significance of the internal forces. 



Again there are species which undergo defoliation at 

 approximately the same time of the year though they are 

 under very dissimilar climates, and one in led to infer that 

 foliar periodicity is inherent and asserts itself no matter 

 what external forces are at work. Many species drop 

 their leaves and remain bare during a period of wet cool 

 weather when the transpiration is probably at a mini- 

 mum. This occurs at Peradeniya with trees of Albizzia 

 procera^ and Pterocarpus echinatus, during the dull moist 

 months of June and July. The periodicity would here ap- 

 pear to be inherent, though there is the possibility that 

 these plants have, in the migration of species, found them- 

 selves at a place where the climate is not in harmony with 

 their original periodicity. 



The feature which impresses a resident in Peradeniya 

 is undoubtedly the great irregularity in the foliar periodi- 

 city of the different trees. It would be very difficult to 

 draw general conclusions as every tree has its own pecu- 

 larities. There is not a month in the year when all the 

 trees are in full foliage, and this can only be explained 

 when we possess a better knowledge of the internal forces 

 at work in every species. 



The most important point, however, rests in the fact 

 that many of our markedly deciduous trees at Peradeniya 

 and still more so in the northern districts of Ceylon, re- 

 main bare only for a part of the hot dry season, and per- 

 haps when the temperature and dryness of the air is at 

 the maximum they burst out into full tender foliage. The 

 output of leaves at any time necessarily occasions in- 

 creased transpiration, but when this occurs at our hottest 



