CHAPTER XXXIV 



RAINFALL 



A GOOD rainfall is of the utmost importance not only foi 

 the growth of the rubber trees but if one is to have first- 

 class yields of latex later on. Water is necessary for the health, 

 the growth, the existence of the Hevea. A tree promptly 

 droops when the water contents of the cells are reduced. In- 

 stead of the stems being erect, and the leaves fresh and green 

 and spread out to the light, the stems weaken and the leaves 

 turn brown and shrivel up. Not only does water serve the 

 purpose of dissolving the salts and other elements necessary for 

 the nourishment and consequent growth of the tree which it 

 receives in solution through the roots, but the tree needs the 

 water itself, and may be as truly said to drink it as any animal 

 does. 



The circulation of water from the soil through the roots of 

 the tree, thence through the sap-wood cells up to the leaves, 

 and thence discharged into the air, is called the transpiration 

 current. Given a sufficient rainfall, the roots of the tree 

 supply it with water as fast as the leaves discharge it into the 

 atmosphere; but when the rainfall is insufficient and the soil 

 parched and dry the leaves give off more than they receive, 

 the sunlight shrivels them up, and they wither away. The 

 stomata of the leaves can prevent only a certain degree of loss 

 of water. The leaves cease to be able to convert the carbonic 

 acid gas derived from the atmosphere into carbon compounds, 

 to work it up into sugars and starch, and the growth of the tree 

 ceases for the time being. 



The bacteria in the soil require moisture as well as air to 

 carry on their work, and when the soil is dry, caked and hard, 

 then activities cease. The roots of the tree suffer as well as 

 the foliage during a continued drought. 



Obviously, the larger the area over which the roots of a tree 



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