<A MONTHLY. \>o 
XXI. COLOMBO, OCTOBER 1st, 1901. No. 4. 
TROPICAL TIMBERS AND THEIR 
RINGS OF GROWTH. 
BY HERBERT WRIGHT, A.R.C.S. 
iEspecialhj written for Indian Gardening and Planting.^ 
HEEE is probably no more in- 
teresting study in timbers than 
that of the seasonal elements 
which a trausverse section of 
the stem exhibits. The majority 
of persons are familiar with 
the historical tables usually 
attached to, or painted upon, 
the successive annular rings of stem sections 
in the museums and gardens of Europe. The validity 
of the idea that each ring counts for a definite period 
of time in the life of the plant is accepted as sound, 
though in past times much controversy was waged 
on the nature of the causes producing these time- 
checking arrangements of the timber elements. The 
bark pressure theories of Sachs and T. Hartig, the 
theory of osmotic variation waged by Russow, and 
the ideas of Weiler and Robert Hartig, respecting 
nutritive supplies to the tree, were all found insuffi. 
cient to explain the nature of the causes which 
determined the formation sf rings of growth. It 
was left to the genius of Strassburger and bis con- 
temporaries to explain the formation of the rings in 
terms of the varying physiological needs of the 
plant. 
In temperate zones the deciduous trees burst into 
new foliage during spring, and the main function 
which the wood has to perform . is that of supply- 
ing copious quantities of water to the growing leaves. 
This is accomplished by the production of large 
lumined, thin walled elements, which form connected 
systems from roots to leaves. During autumn the 
demand for water is not as great, but there is an 
increased weight of plant tissue, and the necessary 
elements to give support and rigidity are added in 
the form of narrow elements possessing Tery 
thick walls. 
The thick walled narrow elements of autumn abnt 
directly on the large elements of the next springj 
and hence the line of demarcation showing the 
limit of growth for any particular year is often very 
conspicuous, The idea that each ring represent 
one year of time is therefore correct for those 
trees in temperate zones which exhibit such period 
icities in leaf production. In the tropics, however, 
where as many as four seasons have each a recog- 
nised power, and the arborescent vegetation is often 
characterised by more than one periodicity in leaf 
production per year, the time represented by each 
ring of growth is not necessarily one year, 
It is obvious to a casual observer that the Tery 
great differences between the periodicities in leaf 
production of the Flamboyant and Cotton trees, or 
those between the Candle, Almond and Para rubber 
trees, or better still between an evergreen having 
no fixed periodicity and a deciduous tree having 
the annual regularity of Schizolobum excelsium — 
sach differences must result in the production o( 
very dissimilar tissue arrangements in the wood o 
the respective trees. We therefore see that in order 
to correctly interpet the " seasonal " rings of growth 
we must know exactly the characterietic periodicity 
and, since the climate and vegetation in the tropics 
are as widely different from those of temperate 
zones, we may expect the problem to assume some 
degree of complicity. 
In tropical countries such as Oeylon, where the 
air is hot and damp throughout the year, the 
majority of trees are usually considered to be of an 
evergreen nature. Many of these ever-greens, such 
as species of Cinnamomum and Eugenia, Mangoe 
