RUBBER AND RUBBER PLANTING 39 



mentioned organs first are, firstly, to hold the tree 

 firmly upright by anchoring it in the soil; and secondly, 

 to absorb certain substances contained in the soil which 

 are essential for the nourishment of the plant Among 

 the most important of these substances, in addition to 

 water, are various compounds of nitrogen, phosphorus 

 and potash. 



Before these substances can be utilised as food by 

 the different parts of the plant, it is necessary for them 

 to be altered and in most cases combined with the still 

 more important substance carbon, which is only obtained 

 through the leaves. One of the most important func- 

 tions of the leaves therefore is to absorb carbon from 

 the atmosphere in the form of carbonic acid gas. The 

 functions of the leaves however are by no means con- 

 fined to absorption. In addition we may compare the 

 leaves to so many minute kitchens or chemical labora- 

 tories, wherein the different ingredients of the food of 

 the tree are prepared and compounded into a form in 

 which they can be utilized and readily digested by the 

 cells that make up the roots, stem and other organs. 

 The energy required for these transformations is derived 

 from the rays of the sun ; and in orcler that the neces- 

 sary chemical changes may be properly carried out, it is 

 necessary for the leaves to be spread out in a position 

 where they are well exposed to air and sunshine. 



We may next pass on to consider the functions of 

 the stem or trunk of the tree. The first of these is to 

 support the leaves in a position well exposed to light 



