68 PLANT DISEASES 



Hartig states that the oospores retain their vitality for four 

 years; hence soil that has produced diseased plants should 

 not be used again. 



Hartig, Unters. aus dem Forstbot. Institut^ 1880, p. 33, 

 i plate. 



De Bary, Beitr. zur Morphol. und Phys. der Pilze, 1881, 



p. 22. 



Hartig and Somerville, Diseases of Trees, p. 38, figs. 



CACAO POD DISEASE 



(Phytophthora omnivora^ De Bary.) 



This disease has been recognised for some years past, 

 but has recently become much more general and destruc- 

 tive to cacao pods in Trinidad. The same fungus is 

 probably the cause of the cacao-pod disease in Ceylon. 



The symptoms of disease are a darkening of the ' shell ' 

 of the pod, which almost invariably commences at one 

 end, and gradually extends over the entire surface. After 

 a while the fruit of the fungus shows on the surface as a 

 delicate white mould, often appearing first in the furrows 

 on the surface of the pojl. 



The white mould represents the conidial form of repro- 

 duction, and lasts for some weeks, the numerous conidia 

 produced being carried by wind to other pods, which in 

 turn become diseased. 



The mycelium of the fungus permeates and destroys the 

 entire substance of the pericarp or ' shell,' and often also 

 attacks the seeds. Numerous resting-spores are formed in 

 the diseased fruit, and are liberated when the tissue decays, 



