110 VEGETABLE PARASITES AND EPIPHYTES 



tree to a shade tree. Its origin in some instances has been 

 traced to the roots of shade trees. 



Stockdale, who has investigated a fungus root-disease 

 affecting cocoa trees in the West Indies, remarks (Fungus 

 Diseases of Cocoa, etc., Pamphlet Series, No. 54, 1908, 

 Imperial Department of Agriculture for the West Indies) : 

 " Trees are rarely killed off singly, but usually in patches. 

 These patches of dead trees, unless something is done, 

 increase in size ; and it has been observed in Dominica, 

 when the disease has been neglected, that areas of nearly 

 an acre in extent have been destroyed. It has been 

 frequently noticed though this is not always the case 

 that these patches, when they are quite small, are cir- 

 cumscribed by the spread of roots from trees that have 

 been used for shade. Pois-doux, bread-fruit, bread-nut, 

 mango, pomme-rose, and avocado pear, which are dead 

 or dying, have been commonly observed in the centre 

 of a diseased area of cocoa, and it has been suggested 

 that the fungus attacks the dead or dying roots of these 

 trees and then affects the young roots of the cocoa. . . . 

 In Dominica it has been found that cocoa has become 

 affected where none of the above-mentioned trees were 

 present, and it was difficult, owing to the length of time 

 that elapsed since the disease first appeared and when 

 investigations were made, to establish clearly at what 

 spot the disease commenced." 



The same writer suspects that more than one species 

 of fungus may be associated with the malady, and that 

 the disease may originate from the fungi found on the 

 decaying logs lying about the plantation. If the latter 

 surmise be correct it is obviously necessary for the cocoa 

 planter to destroy by fire all such logs as well as any 

 dying trees in the plantation. 



Trees affected with the disease should be isolated by 

 digging a trench at least 2 ft. deep and 1 ft. wide around 

 them. The soil taken from the trench should be thrown 

 within the disease-infected area. Trees adjacent to the 

 diseased area should be frequently examined and any 

 which show signs of disease infection should be isolated 

 in a similar manner. Stockdale (loc. cit.) recommends 

 that the whole of the trees in the isolated area should 

 be examined and those most badly diseased extracted 

 and burned. Trees less seriously affected should have the 



