23 
THINNING OUT. 
By E. W. King, 
( Technical Manager , Soviet e Financier e cles Caoutchoucs , Selangor .) 
J" have been asked to read a paper on “ Thinning Out,” paying 
particular attention to points which are open to discussion- 
I think I may take it as granted that everyone agrees with the 
principle of thinning out and that the only points about which 
controversy is probable are: (1) the time at which it should be 
done ; and (2) the extent to which it should be done. 1 have, 
therefore, divided this paper into two parts. The first part showing 
the reasons for it and the second part giving the main lines on 
which I consider it should be carried out. 
PART I. 
Eveiyone has seen the result of trees which have been left closely 
planted. In some cases old nurseries have been left for several 
years with the result that they have shot up into a number of 
long poles with a few leaves at the top, from this to the case 
of a tree planted in the open by itself you get the varying degrees 
of malformation due to insufficient sunlight. The importance of 
sunlight to the health of a plant cannot be too strongly insisted on. 
The two sources of supply of material for the formation of plant 
food are the root system and the leaf system or head. The root 
system supplies water from the soil and soluble inorganic salts, 
which are essential to the health of the tree. The leaves supply 
the bulk of the material forming tlie tissues of the tree. They 
absorb carbon dioxide from the air and by the aid of sunlight 
transform it into starch and other substances needed in the tree’s 
economy. 
As young trees grow they soon fill up with the leaf system 
all the space allotted them. At this period in their life history 
if more space is not given them many consequences follow, the chief 
of which is the reduction in the rate of the growth of the trunk and 
hence in bark renewal. For, since the amount of plant food 
manufactured by the tree is proportional to its leafage and root 
growth, one of the first consequences of a limited growing space 
is that the tree’s food supply does not increase but remains at the 
same amount. It should, of course, gradually increase to correspond 
to the constant demands made by the increased activities of the tree 
as it ages. 
No green plant deprived of light can produce the chemical changes 
on which its proper supply of nutrition depends. Many planters, for 
instance, will have noticed the better growth of clearings with an 
