23 



THINNING OUT. 



By E. W. King, 

 (Technical Matutger, Societt' Financiere des Caoutchoucs, Selangor.) 



X have been asked to i^ad a paper on " Thinning Out," paying 

 particular attention to points which are open to discussion- 

 I think I may take it as gi'aiited that eveiyone agrees with the 

 principle of thinning out and that the only points about which 

 contix)versy 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 caiTied out. 



PAKT 1. 

 Everyone has seen the result of trees which have been left closely 

 planted. In some cases old nursei'ies 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 matei'ial for the formation of plant 

 food are the ixjot 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 the tissues of the tree. They 

 absorb carbon dioxide from the air and by the aid of sunlight 

 ti-ansform 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 fii*st 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 t-o correspond 

 to the constant demands made by the increased activities of the tree 

 as it ages. 



No gi'een plant deprived of light can produce the chemical changes 

 on which its pi-oper supply of nutrition depends. Many planters, for 

 instance, will have noticed the better growth of clearings with an 



