2§8 
THE TROPICAI- AGRICULTURIST. 
[Nov 1, 1902. 
drop and itodacj leaf atiriuK any month ' of the 
year. This is characteristic of Cedrela Toona, Roxb., 
planted in the upsouiitry and a native of Australia. 
There are some species which thongli in the Pera- 
deniya districts are qni'^e deciduous, yet in the 
more equable climate of Java are quite ei'ergreen. 
That the climate of Ceylon has a decided influence 
on the periodicity of the deciduous species is obvious 
if one leaves the Peradeniya district iu May and 
proceeds to the Northern parts of the Island where 
there is very little rain in the S. W. monsoon, and 
where the weather from January to October is 
relatively dry and hot. The defoliation and foliar 
repletion has beeki considerably delayed in the 
Vavoniya and Mannar disiricts compared with 
Peradeniya, the species common to all districts 
dropping their leaves at times which differ by 
many weeks and months. la the northern districts 
so long as the plant drops its leaves duiing any 
of the eight or nine months, the same climatic 
advantages, if any, will accrue. 
It may therefore be concluded that the varia- 
tion which occurs iu the temperature and humidity 
of the air in Ceylon is so great thai it exerts a 
decided influence on the phenomenon of defoliation 
of many of our species. The climatic conditions in 
Ceylon are not equable enough to allow the plants 
to continue their development along a chance line, 
and botanists desirous of studying the personal 
equation of plants should select a more equable area. 
Personal Equation.— Though the climatic effects 
are obvious on many of our species, there are 
several trees which tehave in a manner indicative 
of personal or interval factors being at work. 
Many species drop their leaves and regain full 
foliage at a time which appears decidedly disadvan- 
tageous. Many retain full possession of their 
foliage or put forth the whole of the young tender 
leaves at a time when the physical conditions 
favour maximuu transpiration. Tliese species may 
be less plastic to the climatic forces, or it may be 
that they can achieve their ends in opposition to 
still more severe external forces. 
If one selects trees of Lagerstroemia flosregina, 
Retz; Bridelia retusa, Spreng ; or fpeoies of 
Canarium or Palaquium, he will find that though 
they exist alongside each other under 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 varia- 
tion 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 n-ew leaf and flo ver impresses one with the 
Bignificancd of the internal forces. 
Again there are species which undergo defoliation 
at approxitnately tJie same time of the year though 
they are under very dissimilar climates, and one 
is led to infer that foliar periodicity is inherent 
and asserts itself no matter what external forces are 
at work. Many species drop their loaves and remain 
bare during a period of wet cool weather when the 
transpiration is probably at a minimnra. This occurs 
at Peradeniya with trees of Albizzia procera, Benth., 
and Pterocarpus ochiuatus, Pers ; during the dull 
moist months of June and July, The periodicity 
would here appear to be inherent, though there is the 
possibility that these plants have, in the migration 
of species, found themselves at a place where the 
climate is not in harmony with their original 
periodicity. 
The feature which impresses a resident in Pera- 
deniya is undoubtedly the great irregularity in the 
foliar periodicity of the different trees. It would 
be very difficult to draw general conclusions as 
every tree ha^ its own peculiaritie. There is not 
a month in the year when all the ""ees are inful 
folipgo, and thl? can only be explained when we 
possess a bettor kiiowledge of the internal forces 
at work iu tvery specisa, 
The moat important point, however, rests in th 
fact that many of our markedly deciduous tree 
at Peradeniya and still more so in the northern 
dist-icts of Ceylon, remain bare only for a part 
of the hot dry, season, and perhaps when the tem- 
perature and dryness of the air is at the maximum 
they burst out into full tender foliage. The out- 
put of leaves at any time necessarily occasions 
increased transpiration, but when this occurs at our 
hottest and driest time the transpiration is probably at 
the maximum. It is therefore very difficult to 
corre'ate the deciduous phase with the theory of 
checking transpiration in every instance, and in 
these cases we must look for other forces which are 
probably internal, e g., Stereospermum suavolens 
D.C., Spondias mangifera, Willd., and Aziadiraohta 
indica, A. Juss. We will now proceed to discuss the 
significance of foliar periodicity and the assistance it 
gives towards a true interpretation of the histological 
differentiation of the secondary xylem. 
Complete defoliation and foliar repletion usually 
resulis in the differentiation of rings of growth in the 
wood of the stem. In temperate zones the pheno- 
menon is annual, and when such is the case, each 
ring of growth represents one year of time. 
In Ceylon and the tropics generally the fall of 
leaf and production of new foliage is often more 
than once per year, and is further subject to varia- 
tions according to the internal requirements of the 
particular plants. It is therefore obvious that at 
least a knowledge of the exact periodicity of every 
species must be at hand before we can interpret 
the time value of the rings of growth. 
For convenience we may first describe the 
periodicities of trees belonging to the deciduotis 
class. 
The sapling stage, often including the first few 
years of the plant's life, is reported to le of con- 
tinuous growth, but in many species, notably 
Eriodendron aufractuosum, defoliation occurs during 
the first year and a ring of growth is presented in 
the stem. In species where there is no such 
differentiation the central wood must represent an 
unknown number of years. In most of our mature 
trees the foliar repletion occurs once per year, but 
in others such as Terminalia Catappa, Stereospermum 
chelenoides, Pithecolobium Saman, it occurs oftener, 
and each period of foliar activity must needs be 
represented in the stem. Many trees undergo foliar 
depletion at irregular intervals of time, probably as 
a result of successive years of drought or purely 
personal reasons, and in each case a complete 
knowledge of the life history of the plant is necessary 
before the differentiations in the xyiem can be ex- 
plained. 
Then again I have seen Portlandia grandiflora 
completely defoliated by an insect as soon as it 
came into new leaf, and several weeks were required 
for a complete renewal to be efiected. If my 
information is correct that this tree undergoes this 
cycle every year, the rings of growth should be double 
those of an undisturbed tree of the same species. 
Similary there are certain trees of Bombas mala- 
barium at Peradeniya which are completely defoli- 
ated by the ravages of the flying foxes which an- 
nually visit the district. These animals appear 
after the trees have completed their annual output 
of leaves and remain until all the foliage has been 
devoured ; by this time the other trees of this species are 
just beginning to drop their leaves and a curious sight 
is then presented. Those trees which have been 
defoliated by the flying foxes now burst out into 
new leaf for a second time that year, and as thi 
goes on from year to year, a comparison of th 
rings of growth in the stems of such trees wi 
those which are never thus defoliated should pro 
highly interesting. Probably many other trees suff 
defoliation from like causes and it is obvious th 
a knowledge o£ the life history of each plant 
UQce^sary before the timc-valae of each ling of gra 
can be detei'ifiined. 
