154 COCOA 



CHAP. 



plant is, however, often misunderstood. At first sight 

 it may seem obvious that, when a definite part of the 

 soil is destined for one cocoa tree, this tree will not 

 obtain so much food if a certain number of weeds also 

 feed on the same spot, as it would if it stood quite 

 alone. And of course it is the case that the weeds 

 take different constituents from the soil, namely : (1) 

 solid plant-food (salts of potassium, etc.); (2) water; 

 and (3) oxygen. Let us see to what extent this robbery 

 by weeds prejudices the cocoa tree. 



The solid plant-food taken by the roots of the weeds 

 from the soil is deposited in the stem, the leaves, the 

 flowers and the fruits of the weeds. It is true that a 

 certain amount of this food is always lost when the fruit 

 or seeds are carried away by the wind, or by birds or other 

 animals; but, on the other hand, seeds and fruits from 

 other places (or their constituents) are probably de- 

 posited on the spot by the wind and by means of the 

 excrement of other birds. It may be said, therefore, 

 that no loss of solid plant-food results in the end. 

 Further, if the weeds are cut down before they have 

 had time to make seeds, no solid plant-food at all goes 

 to other places, and the stems and leaves of the rotten 

 weeds and their constituents return again into the soil. 

 Even more, indeed, is restored to the soil than was 

 taken out, so that there is no loss but a gain ; for in 

 addition to the compounds just mentioned, which were 

 originally taken from the soil, the weeds also contain 

 other compounds in the leaves and stems, which were 

 made by the plant from the carbon dioxide of the air. 

 These contain mainly carbon and oxygen, and c6nstitute 

 even the greatest portion of the plant. They are called 

 the " organic constituents," and when they are in- 

 corporated into the soil they form the humus. These 

 facts may be summarised as follows : The plant takes 

 different salts from the soil ("inorganic constituents") 

 e.g. salts of potassium, phosphoric acid, etc. and also 

 forms "organic constituents" e.g. sugar, amylum, 

 albumen, etc. by means of the carbon dioxide of the 



