96 VEGETABLE PARASITES AND EPIPHYTES 



years that specific cocoa diseases have been systematically 

 studied. 



It is probable, therefore, that the majority of the 

 recently discovered diseases have been present in cocoa 

 plantations for many years. 



In conjunction with the study of the life-histories of 

 the fungus parasites responsible for these diseases, 

 considerable information has been acquired in regard to 

 remedial treatment, which has satisfactorily demonstrated 

 that practically the whole of them are amenable to treat- 

 ment. Many diseases which had become rampant were 

 rapidly reduced to a minimum by careful, systematic 

 treatment. It is considered that the additional ex- 

 penditure which the remedial measures involved was more 

 than compensated for by the increased crops produced 

 as a result of the improved sanitary condition of the 

 trees. 



Canker Disease, Nectria sp., in Ceylon. A parasitic 

 fungus disease, termed canker, was observed in Ceylon 

 cocoa plantations in 1889, and Carruthers subsequently 

 investigated the life-history of this pest and suggested 

 remedial measures (Circular, Royal Botanic Gardens, 

 Ceylon, No. 23, 1901). The fungus was referred to the 

 genus Nectria, and on estates where the suggested remedies 

 were adopted the spread of the disease was appreciably 

 checked. This is still the most serious disease which 

 affects cocoa in Ceylon. The mycelium of the fungus 

 is rapidly diffused through the stem and branch 

 tissues, but infected trees may live for months, and 

 even years. 



The symptoms associated with this disease are : a 

 reduction of the crop, dying-back of branches, and a 

 general lack of vigour in the tree. 



Affected parts of the stem and main branches are 

 often indicated by moist, dark patches on the bark. If 

 such areas be excised the interior tissues of the bark will 

 be found discoloured brown or reddish, in marked con- 

 trast to the much paler colour of healthy bark. 



If the disease be allowed to develop, a gummy matter 

 frequently exudes through the bark of the affected parts. 

 Pustules of white or pinkish spores eventually appear on 

 the bark, which are carried about by wind, insects, and 

 other agencies, and further disseminate the disease. 



