95 



The difficulties associated with the attempts to ex- 

 terminate epidemic fungus diseases are amply demon- 

 strated by those adopted with regard to " Vine mildew," 

 Plasmopara viticola, De Bary, " Wheat rust," Puccinia 

 graminis, Pers., and " Coffee-leaf disease," Hemileia 

 vastatrix, Berk. The necessity for adopting preventive 

 measures by maintaining sanitary conditions in the 

 plantation cannot be too strongly urged. Proper culti- 

 vation, selecting beans from disease-resistant plants, 

 and the burning of diseased tissues are all prophylactic 

 measures which also merit general adoption. 



A stock of reliable fungicides, such as those recom- 

 mended towards the end of this chapter, should always 

 be kept, as well as suitable apparatus, such as sprayers, to 

 apply them. A disease treated in its early stages usually 

 may be checked and even extirpated, whereas this may 

 be impossible if it be allowed to become rampant. 



Vegetative and Reproductive Organs of Fungus Parasites. 

 Fungus diseases are most largely disseminated by means 

 of spores ; these for all practical reproductive purposes 

 may be considered to take the place which seeds occupy 

 in regard to flowering plants. Some forms of parasitic 

 fungi, however, rarely produce spores, and perpetuate 

 themselves by hibernating mycelium. 



Spores are minute bodies, many thousands of which are 

 required to cover a threepenny bit. They vary greatly 

 in size and colour, and are produced in enormous quanti- 

 ties, which are readily distributed by wind, rain, insects, 

 animals, man, and numerous other agencies. Any which 

 happen to alight on a suitable host germinate, and, if the 

 conditions favourable to their development be present, 

 spread disease. The most propitious conditions for the 

 development of parasitic fungi are heat and mois- 

 ture. Sunlight generally acts as a deterrent, so that 

 closely planted cocoa trees afford more encouragement 

 to disease diffusion than those planted wider apart. 



The blights mentioned in old writings referring to 

 cocoa, were doubtlessly mainly due to fungus diseases. 



De Verteuil, in his book on Trinidad, writes : " But 

 in the year 1727, according to Gumilla, not a disease of 

 the trees, but a blight, attacking the pods (fruits) under 

 certain atmospheric influences, destroyed the crops." 



It is, however, only within the last thirteen or fourteen 



