220 
THE TROPICAL ^ AGEICULTURIST. [Oct. 1, 1901. 
and Jak, etc., have no fixed periodicity, and new 
leaves may occur any month in the year ; others 
produce leaves at a definite time each year, and of 
this class the most conspicuous are the ebony trees. 
Further, it is worthy of note that those trees of 
Diospyroa embiyopteris and Biospyros Gardneri, 
which as yet have not produced sexual organs, are 
invariably characterised by a biannual foliar period- 
icity. A comparison between the rings of growth 
of a young ebony — not flowering — and one regularly 
producing flowers, should therefore prove highly 
interesting. Next to the evergreens we may for 
comparison place those trees which drop their old 
leaves simultaneously, but which have produced leaf 
buds prior to the fall of the old ones, as in Dillenia 
indica, Ehopalocarpus lucidus. etc. Many others 
however, have gone a step further, and the pro- 
duction of new leaves is delayed until the greater 
part of the old leaves have dropped and the tree 
assumes a semi-bare condition, as in Fious Trimeni. 
Continuing in this direction we come next to those 
trees which, like the Inga saman ond Candle, are 
bare for a few days, and finally to those like Ery- 
thrina umbrosa, Careya arborea, Bombax, Hevea 
brasiliensis, Dalbergia frondosa, Plnmieria acutifolia 
and a host of less familiar trees wlaich remain 
leafless for several weeks or months during every 
year. 
There are very few species in Ceylon which drop 
their old leaves and produce new foliage more than 
once per year, a notable exception being the almond 
— Terminalia catappa. 
Not only does the foliar periodicity vary with 
the species, but trees of the same species exhibit 
'great variability, and it is even doubtful whether (he 
the same tree produces new leaves at exactly tfc« 
same time from year to year. These differences 
must be due either to the varying personal require- 
ments of the plants or the environment under which 
they exist. 
In studying the personal equation of the plant one 
cannot but conclude that one of the foremost objects 
in dropping the leaves is to check excessive trans- 
piration. In the Peradeniyi districts and in all 
those parts of the island which feel the dry heat 
of the N.-E. Monsoon, many of the deciduous trees 
drop their leaves before or during the hottest mouths 
—February to April and thereby avoid a condition 
of transpiration which might otherwise prove fatal, 
The noteworthy examples are Crataera Eoxburghi, 
Erythrina indica, Ficus Amottiana, Sterculia balan- 
chos, Schizolobium excelsum, Oroxylum indicum, 
Cnpania edulis, Antiaris innoxia, the Cotton and 
Para and Ceara rubber trees and many others fami- 
liar to the tropical tourist. That this is one of the 
prime objects is further indicated by the behaviour 
uf Careya arborea, Eriodendron aufractuosum, and 
others in the Eibile and Batticaloa districts, since 
in these places the production of new leaf is delayed 
considerably— an obvious advantage where the S.W. 
Monsoon is replaced by hot dry weather. If it were 
necessary to bring proof in support of this idea, 
one need only point out the behaviour in desprt 
areas where those plants, the tissues of which are 
neither fleshy nor protected by hairs or other con- 
trivances, drop their leaves prior to a period of 
drought. The zerophytic plants having leaves which 
either in virtue of their iucculence retain for a long 
time the greater part of the water they have ob- 
tained, or are so protected by hairs, wax, cuticle, 
sunken stomata, etc., that loss of water by trans- 
piration is at a minimum, such plants remain ever 
green throughout the hottest months. The plants 
not so adapted must necessarily drop their leaves 
in order to prevent excessive loss of water. In tem- 
perate zones a reversion is seen, since it is during 
the cool months that the trees become bare, and 
only when heat and sunshine present their maxi- 
mum strength that the arborescent vegetation puts 
qU the best show of leaf. 
One of the reasons why, in temperate zones, the trees 
drop their leaf in winter is probably to be found in 
the fact that the soil is bo cold .that absorption 
cannot take place through the loots, and hence no 
supply being guaranteed, the plants lose their foli- 
age until the warmer weather arrives. 
Though the checking of transpiration seems to be 
one object, it is rather surprising to notice the 
comparative zerophytic nature of the leaves of Ficus 
Arnottiana, Ficus Trimeni, and others where the 
transpiration is probably much less than that from 
the tender leaves of Brownea grandiceps, and yet 
the former are deciduous and the latter is evergreen. 
Further, we have to face the difficulty that the 
hottest part of the year is not that chosen by all 
the deciduous trees, as is instanced by the behaviour 
of Albizzia procera and Dalbergia frondosa, which 
become bare in the Peradeniya districts during the 
dull wet month of July when transpiration cannot 
be at all excessive, But what is still more 
difficult to bring into comformity with the theory 
of checking transpiration is the production of abun- 
dance of fresh foliage when the dry heat of the 
N.-E. Monsoon is asserting its maximum power. 
This occurs with trees of Sderocarya caffra and 
Terminalia melanocaipnm during the hot month of 
March, and similarly Sterculia balanchos and 
Chlorocylon Swietinia in April. It is highly prob- 
able that many of these trees have, in the migra- 
tion of species, found their way into districts where 
the climate is not in agreement with their old 
periodicites. They may, or may not, acquire a new 
periodicity, and it would be important if we could 
determine whether the periodicity of imported 
species grown from Feed remains the same as in 
the native districts. One might also notice whether 
a species, native of our country, shows the same 
periodicity as locally grown trees when introduced 
again from abroad. 
Many of the peculiarities will probably have to 
be explained on purely personal grounds, since they 
do not lend themselves to correlation with known 
environments. The power of the personal equation 
can be better studied in the tropics than in temperate 
zones, since the variation of season has such a pre* 
ponderant influence in the latter areas. 
Many instances are known which point to the 
operation of purely individual forces within the 
plant. In Java et ses Habitants, by I. Ohailley-Bert, 
mention is made of the fact that trees of the" same 
species of Palaquium are growing side by side and 
under conditions almost identical, and yet one may 
be bare at a time when the others retain full poss- 
ession of their foliage, 
Mr. Nock also informs me that the English oaks 
grown at Hakgala under a comparatively temperate 
climate behave in the same irregular manner. This 
individual variation cannot be better studied than 
at Peradeniya, where Lagerstroemia flos-regina, a 
native of the moist lowconntry of Ceylon, grows 
in abundance. Here, in the month of February, 
one tree was perfectly bare and yet others only a 
few yards distant were in full foliage ; others were 
about to drop their leaves, and during the same 
month one had not only dropped its foliage, but 
burst into new leaf and followed this by production 
of flowers. Similarly with trees of Bridelia retusa, 
also a native of the moist lowcountry. So much 
then to indicate that internal factors may be at 
work in determining periodicity of leaf production, 
On the other hand, there is considerable evidence 
in the acclimatisation of trees that the power of 
environment is very great. A moment's consideration 
of the powerful influence of a temperate climate 
on the phases of vegetation is alone sufficient. 
There are instances which seem to point to the 
possibility of a new periodicity, without the loss of 
the old one, being produced by a change of climate. 
Here we must content ourselves with a few examples 
which indicpite the jaower p£ climate. One case of 
