THE SYMPTOMS OF CANKER IN COCOA 99 



dry, greyish-brown aspect. The diseased bark is most 

 evident during the dry season immediately after a shower 

 of rain, as it does not dry so rapidly as healthy bark. 

 During the early stages of the attack the bark, when 

 cut, shows only a slight discoloration, but when the 

 disease is more advanced a cut reveals a deep claret 

 coloration. In the latter condition the bark is soft 

 and moist, and the exterior, woody tissue is usually 

 aiiected and assumes a dark brown colour. A brownish- 

 red, gummy fluid subsequently oozes out of cracks which 

 form in these areas ; this is known as the bleeding stage. 

 The dried, gummy exudations impart a rusty appearance 

 to the bark. 



Branches are frequently kiUed by becoming " ringed " 

 with the canker, and even whole trees are destroyed when 

 the disease affects the trunk near the ground. 



One of the effects of canker on cocoa trees in Dominica 

 is the production of an abnormal number of flowers which 

 do not mature fruit. Cocoa trees which annually produce 

 a phenomenally large number of flowers, and have never 

 been known to produce mature fruits, have been observed 

 by the writer both in the Gold Coast and in San Thome ; 

 in these instances this was purely a teratological char- 

 acter, as the trees exhibited not the slightest trace of being 

 diseased. 



The fructifications of both Nectria Theobromce and 

 Calonectria ftavida usually may be found on diseased bark 

 during the rainy season. 



Two forms of spores are produced, viz. conidiospores and 

 ascospores. The former appear first in the form of white 

 pusttdar-like mould through cracks in the diseased bark. 

 Later in the same places, colonies of perithecia appear. 

 A single perithecium is about the size of a grain of red 

 pepper and contains numerous asci in which the ascospores 

 are placed. The perithecia of Nectria Theobromce are 

 red, whfle those of Calonectria flavida are yeUow. 



The preventive and remedial measures to apply to these 

 parasites are simflar to those suggested with reference to 

 the canker disease of cocoa in Ceylon. 



Die-back and Brown-Pod Disease, Thyridaria tarda. — 

 For the following remarks on this ubiquitous cocoa 

 pest, the writer is indebted to Mr. H. Bancroft, of 

 the Jodrell Laboratory, Royal Botanic Gardens, Kew : 



