156 COCOA 



CHAP. 



amount of evaporation the greater. This has been 

 elucidated by special experiments, and it has been 

 demonstrated that on a soil with plant growth the 

 evaporation is greater than on a soil without plant 

 growth. 



Accordingly, in a plantation with weeds the evapora- 

 tion is greater, and in times of drought the cocoa trees 

 will suffer more from drought than in a plantation 

 which is free of weeds. This fact cannot be emphasised 

 too strongly, because so much misunderstanding exists 

 in regard to the question, not only among planters but 

 also in handbooks. For instance, Chevalier's excellent 

 book l recommends the planter to leave the weeds 

 standing during the dry season, and even to plant some 

 catch-crop plants such as beans, taro or sweet potato 

 at the end of the rainy season. Apart from the fact 

 that beans and sweet potatoes would not grow under 

 shade trees, the result of this would only be that the 

 cocoa would suffer still more from drought. The 

 practical and interesting little book by Olivieri 2 also 

 gives currency to the erroneous opinion that the 

 " destruction of grass tends to increase exposure and 

 dry ness." 



In connection with these facts it may be pointed out 

 that a tree without leaves evaporates less water than a 

 tree with leaves, and it is therefore an advantage to 

 have a species of shade tree which defoliates in the 

 dry season. This fact is also often misunderstood, and 

 even some authors on cocoa incorrectly assert that a 

 shade tree should keep its leaves during the dry season 

 in order to keep the soil moist. 



Finally, we have to deal with the influence of weeds 

 on the aeration of the soil a very important point. 

 Every part of every living plant needs oxygen from 

 the air ; day and night the leaves, the stems, and the 

 roots of the plants absorb oxygen from the air and 

 return carbon dioxide. This is the respiration of plants. 



1 Chevalier, Le Cacaoyer dans VOuest africain (1908), p. 122. 

 2 Olivieri, Treatise (1903), p. 82. 



