Notes . 
595 
year ; others exhibit periodic increase in foliar activity several times 
per year, in addition to a complete annual renewal, and many intro- 
duced species show great variation during their phase of acclimatization. 
In the northern districts, where the rains of the south-west monsoon 
are very feeble as compared with those at Peradeniya, the defoliation 
is considerably delayed. The climatic conditions in Ceylon are not 
equable enough to allow continued development along personal lines, 
and botanists desiring to study the personal equation in plant life 
should select a more equable area. 
Internal forces are, however, obviously at work, as evidenced by the 
following facts : — 
(a) Species retain full possession of their foliage or put forth new 
leaves when the temperature and dryness of the air is at the maximum. 
(< b ) Some species drop their leaves and remain bare during our wet, 
cool months, when transpiration is at the minimum. 
(c) Plants of the same species, on the same plots, are deciduous at 
periods varying by many weeks and months. 
(d) The same species may undergo defoliation at approximately 
the same time of the year, though under the dissimilar climates of 
Peradeniya, Colombo, and Mannar. 
The irregularity of foliar periodicity is very pronounced. There is 
not a month when all the trees are in full leaf. 
The foliar periodicity of the evergreens is as complex as that of the 
deciduous trees, the foliar renewal taking place annually, semi-annually, 
or at other periods, all being subject to individual variations. 
Complete defoliation and foliar renewal in temperate and tropical 
zones often results in the differentiation of rings of growth in the 
secondary xylem. The variation in our tropical species is so great 
that an exact knowledge of foliar activity must be at hand before the 
time-value of the rings of growth can be determined. Saplings may 
undergo foliar renewal in the first year, or several years may elapse 
before this occurs ; mature plants may be characterized by annual, 
semi-annual, or periodic intervals of leaf production ; further, many 
trees are repeatedly defoliated by the ravages of insects, bats, and 
Fungi. 
Foliar periodicity is the most potent factor in determining the 
number and significance of the rings of growth, but for the complete 
interpretation of these a further knowledge of the rate of cambial 
activity and the independent effect of a hot dry season is necessary. 
