Nov. 1, 1902.] THE TKOPICAL 
Now consider the evergreen trees. For onr purposes 
an evergreen tree may be defined as one which 
never becomes even partially bare so long as it is 
free from disease. Tliere can be no sharp line between 
trees beloQoiiig to the evergreen or deciduous classes. 
The evergreen trees are continually putting on new 
leaf, and though the older leaves gi adually fall cff, the 
nett result is usually an increase of "foliage horn 
year to year. 
The young trees usually put on nfw leaves at a snc- 
oessively inereaEing rate from year, to year, but when 
mature a regularity in output often asserts itself. 
In a large number of our species the foliage is 
added at one or more times every year, and in such 
e.f/- Maugifera indica, L., definite rings of 
growth are produced every year. The output 
of new foliage leads to an increased trans- 
piration, and this may or may not lef d to the 
differentiation of a ring of growth. The trees which 
show an annual output of leaves at a parlicular 
time are invariably mature and floweis follow in 
the axils of the new leaves. In young, non-floweriDg 
evergreens, however, the fcliage is often added in 
two parts, one in the N.B. and the other in the 
S.W. monsoon. Evergreens characterised by such 
a bi-annual foliar periodicitj' are comparable to the 
deciduous Terminalia Catappa trees, and t'lo rings 
of growth in them probably number more than one 
per year. There are, however, a very large number 
of evergreen trees which have no fixed foliage perio- 
dicity but put on new leaf every week or month 
of the year. Among these we have several species 
of Eugenia, Artooarpus and Cinnamomum, and 
numerous others, the rings of growth of which, 
when present, lequire a deal'of consideration before 
a correct elucidation can be given. 
Finally, there are evergreen trees which though 
they produce a large number of leaves at a parti- 
cular time e ch year, are continually putting forth 
new leaf buds during the reniainirg mouths of the 
year. It is further conceivable under equable 
physical conditions, for the same tree to change its 
mode of leaf production from time to time, in 
which case a knov/Iedge of the personal equation 
of the plant would be of the utmost importance. 
The point whieh we have to notice is, that, 
providing there is a special period at which the 
evergreen cr deciduous trees put forward their leaf 
for the year, this will result in an especial amount 
of transpiration for that period. This is ususlly 
followed by the differentiation of large Inmined 
thin walled tracheal elements, and each ring of 
growth thus established is a record of past foliar 
activity. 
The tendency is to produce a very distinct ring 
of growth in those deciduous trees which are 
bare for very long periods, though this by no means 
prevents very slow growing evei greens from pi'oducing 
rings of varying significance. There are, however, 
many deciduous trees which show very poor riugs 
of growth, and on the other hand eveigreen trees 
with very pronounced rings in the secondniy xylera. 
This brings us to the other factors which determine 
the significance, and in some cases, perhaps, the 
actual formation of rings of growth in our tropical 
■woods, 
The^'O factors are 
(1) i.. . ' of cambial activity. 
('2) ludep^. ■■'t effect of a hot dry climate. 
DATE OF CAMBIAL ACTIVITY. 
An erroneous popular notion exists that in Ceylon 
the deciduous trees are usually of more rapid 
growth than the evergeens. This probably has its 
origin in the fact that the deciduous trees which are 
most conspicuous are the plentifully distributed mem- 
bers of the !\Ialvacea3 and Euphoibiacete which attain 
enormous dimensiouis. 
i No such relationship exists, however, and the rate 
of cambial activity is of great variation in trees of 
both classes. 
AGBlCULTUftlST, 
On the one hand the qnickc&t growing tree in 
Ceylon is Albizzia lilollucana, an evergreen, while 
quick growing trees such as Melia dubia and Bonibax 
malabarium are markedly deciduous. On the o her 
hand the Sapotacf co and Ebenacm include some of 
our slowest grrwing trees and though the majority 
are evergreen, there are a few which nro deciduous; 
similary sljw growing tree? in the form of Bridelii 
retusa, and Ciataevce Roxbni'ghii are decidedly 
deciduous. Hence no definite relationship exists in 
this connection. 
Nevertheless the rate of cambial activity is an 
important factcr in determining the significance of 
the rings of growth, and ai active meristematic 
layer is probably the cause of the ring^ being 
more prominent in a quick growing evergreen thaa 
in a slow growing deciduous tree. 
Consider first the rate of cambial activity in the 
deciduous pl'.nts. Here we will consider trees which 
are decidous at approximately the same time of the 
year for about the same lecgth of time. Our best 
examples of quick growing trees are Bcmbnx Mala- 
barium and "Eriodendron aufractuosum. In these 
species the rings of growth are very conspicuous 
and may measure several inches in diameter, 
Crataevoo Boxburghii is a species character- 
ised by a slow rate of camb'al activity, and 
the stem does not attain a diameter of six 
inches in twenty years. The rings of growth are 
here very inconspicuous though the tree is bare for 
four to five mon''hs every year, in this species 
the leaf fall takes place at a remarkably slow rate, 
the discoloured leafless first beginning to drop on 
26ih August, though the tree does not become 
absolutely leafless until the middle of October each 
year. Similarly the output of new leaf proceeds at 
a very slow rate, and consequently the rings of 
growth are inconspicuous. 
A complete list of plants can be quoted to show 
that the significance of the rings of growth in 
stems of deciduous trees is in proportion to the rata 
activity of the vascular cambium, providing other 
conditions are the same. 
Similary with the evergreen trees which put on new 
leaf durinsj the same months of the year, moderately 
quick growing trees such as Maugifera indica, 
show definite rings of growth ; whereas our 
slow growing species Palaquium and Diospyroa 
(trees which sometimes do not exceed a diameter 
of six inches in 60 years) the rings are very 
poorly defined. 
The importance of the rate of cambial activity 
is best realised, however, if we compare the rings 
uf a moderately quick growing evergreen and a slow 
growing deciduous tree, say Maugifera indica and 
Cr ataevaj Koxburghii ; for though the latter is bare 
for so very many weeks every year, its insigniticent 
rings cannot be compared with the broad bauds in 
the wood of the former. 
The independent effect of climate is very difficult 
to determine since the significance of the rings of 
growth is in part a consequence of additional 
factors, viz., rate of cambial activity and foliar 
periodicty, which it is impossible to eliminate. 
The ideal conditions would be, where a hot drought 
of three or four months is followed by continuons 
rain for the remaining eight or nine months, and 
evergreen trees having no seasonal periodicity or a 
deciduous tree undergoing complete defoliation and 
repletion in the middle of either period of drought 
and rain. Trees approximating to the former elass are 
to be found in certain Cinnamomum species, and 
of the latter class in Terminalia Catappa, 
though neither of tliese nor the climate in Ceylon 
are in exact accord with the theoretical condition 
desired. 
Nevertheless, an evergreen tree having no fixed 
periodicity but continually putting fortn a regular 
supply of leaf when subject to such a climate 
would provide good material for determining the 
part which a strongly marked climate pla3-3 ia tha 
