234 COCOA CHAP. 



written at present ; all that can be done is to give a 

 summary of the present state of our knowledge. 



THE CAUSES OF DISEASE. Every tree which is not 

 in healthy condition may be called diseased. When 

 the soil is too poor, when the plant is damaged by wind 

 or by sudden lack of shade, when the drainage is in- 

 sufficient, or any other harmful condition of cultivation 

 is present, the tree may be considered to be a subject 

 for the pathologist. Still these kinds of disease need 

 not be described here : they are avoided when correct 

 methods of cultivation are applied. But there are 

 other diseases which damage the fields in spite of the 

 best methods of cultivation, and which attack perfectly 

 healthy trees just as readily as the weak ones. The 

 cause of many of these diseases was formerly a complete 

 mystery to practical planters, who gave them names 

 without real significance, such as " blight," or " blast," 

 or " rust/' or " die-back." Botanists have discovered, 

 however, that most of them are caused by fungi which 

 penetrate into the tissue of the plants and kill or at 

 any rate damage it. These diseases are therefore 

 contagious, because the fungus by means of its spores 

 can spread from the diseased plant to a healthy one. 



Apart from this large group of diseases due to fungi, 

 there is another large group caused by insects. These 

 were generally better understood by the planter, who 

 was often able to detect the cause without any scientific 

 aid. Sometimes, however, this was not the case. In 

 Surinam, for instance, the so-called "leaf disease" was 

 well known to the planters for a long time without their 

 suspecting that it was caused by an insect (thrips). 



Finally, the cocoa tree is in all countries more or less 

 damaged by larger animals, chiefly birds and mammals. 



CLASSIFICATION OF DISEASES 



The external symptoms of the different diseases 

 and pests are not sufficiently characteristic to allow of 

 a clear classification being based upon them. In this 



