108 VEGETABLE PARASITES AND EPIPHYTES 



a scabby appearance ; small, blackish, corky patches 

 being produced on the surface. Such fruits do not 

 properly develop, and they do not usually decay, but 

 the beans are frequently smaller than those of healthy 

 fruits. Specimens of diseased roots and stems of cocoa 

 were examined by the Mycologist of the West Indian 

 Department of Agriculture. Large numbers of septate, 

 dark-coloured mycelial threads were found in the vessels 

 of the roots, as well as in the vessels, medullary rays, 

 and other cells of the stems. 



Trees affected with this disease in Dominica lack 

 vigour, present a dwarfed appearance, and the branches 

 die back. Blackish fructifications have been noticed 

 pushing through the bark. Cankered trees have been 

 observed in Grenada, where Lasiodiplodia appeared to be 

 following the old canker-affected areas. Canker is, 

 however, attributed to this disease in Trinidad. 



Manuring and high cultivation have been attended 

 with good results in regard to cocoa trees affected with 

 this disease in Dominica. It is generally found in districts 

 where the soil is not weU suited for the cultivation of 

 cocoa. Where the fungus causes canker it should be 

 attacked by the measures already suggested with refer- 

 ence to cankered trees. If it attacks the fruits and causes 

 the branches to die back the remedies recommended in 

 regard to Thyridaria tarda might be applied. 



Black Rot of Fruits, Phytophthora omnivora, De Bary. — 

 This disease is ubiquitous in cocoa plantations in both 

 Trinidad and San Thome, and has also been found attack- 

 ing cocoa in St. Lucia, St. Vincent, British Guiana, and 

 Surinam. Affected fruits are turned black and become 

 covered with the mycelium of the fungus. The ovate 

 conidia borne upon the mycelium are carried about by 

 the usual agencies, and disseminate the disease. Conidia 

 which fall on fruits germinate, and if the conditions be 

 favourable, penetrate the fruit-waU. The fungus mycelium 

 then rapidly spreads through the tissues and frequently 

 destroys the fruit. The latter becomes black and hard ; 

 it may hang on the tree for a considerable time and is 

 eventually enveloped in white mycelium and conidia. 



Resting spores (oospores) are formed by a sexual process 

 within the fruit, and these are liberated when the latter 

 decays and still further aid in spreading the disease. 



