78 DISEASES 



and the latter absent in its new home. Again, the 

 hygienic conditions may be more favourable to the 

 development of various fungus parasites ; its vitality 

 may be weakened by soil or climatic agencies or by 

 methods of cultivation. 



It is universally acknowledged that plants like the 

 cocoa tree, whose habits have been altered, or " im- 

 proved " from the planter's point of view, by long periods 

 of cultivation, are more subject to disease than the wild 

 types of the same species. That the constitution of 

 the cocoa tree has been altered by introduction to, and 

 cultivation in, new countries, is amply exemplified by 

 the numerous varieties and forms now extant. 



It wiU therefore be apparent that it is incumbent 

 on the cocoa planter to adopt every possible means in his 

 power to prevent the introduction of disease into his 

 plantation, and when it does appear, to take immediate 

 steps to eradicate it. 



The difficulties attending the prevention and exter- 

 mination of disease from a permanent crop, such as cocoa, 

 are far greater than in the case of an annual crop, for with 

 the latter a change of crop wiU invariably produce the 

 desired results. The cultivation of certain inter-crops 

 and catch-crops with cocoa might tend to check disease 

 diffusion ; and belts of trees, planted at suitable distances 

 apart throughout the plantation, would serve both to 

 protect the cocoa trees from wind and deter the spread 

 of disease. 



For the reasons already mentioned the species chosen 

 for the inter-crops, catch-crops, or wind-shelter-belts 

 should be selected from those belonging to different 

 natural orders of plants from those to which the cocoa 

 tree belongs, viz. StemUiacece. 



The living organisms associated with the diseases of the 

 cocoa tree may be divided into two groups, i.e. animals 

 and plants. 



Of the vertebrata which are inimical may be men- 

 tioned man, monkeys, deer, squirrels, and rats. 



It is, however, among the invertebrata that we find 

 the most pernicious pests of the cocoa tree, such as beetles, 

 the larvae of beetles and moths, thrips, aphis, etc. 



Plants as factors of disease in cocoa trees can be separ- 

 ated into two series, the flowering plants, Phanerogams, 



