DISEASES OF CACAO 95 



A circular brown patch makes its appearance, which gradually extends all 

 over the pod and oausea complete deatruotion. Microscopic examination shows 

 that the cells are filled with colourless septate branched mycelium. When 

 the diseased patch on the rind is about the size of a penny-piece, small circular 

 mounds about the size of a pin's head can be seen about the centre of the 

 brown area of the rind, from which a greyish-white powdery dust is expelled 

 which turns black in a, short time. This dust is composed of elliptical dark- 

 brown one-septate spores measuring on the average 20 x 10 microns. The 

 small mounds are found to be due to the pyonidial fructifications of a fungus 

 in which the spores are formed, which rupture the epidermis and liberate the 

 sporesthroughasmalloircularopeningorostioleat the apex of thepyonidium." 



The same observer carried out many infection experi- 

 ments on different forms of host, several of which have 

 been duplicated by the writer with confirmatory results. 



He discusses the systematic position of the fungus in 

 the West Indian Bulletin, vol. ii. p. 195, in which he 

 refers it, as others had previously done, to " Fungi, 

 Imperfecti," which means a fungus whose life history has 

 not been fully worked out, and consequently cannot be at 

 present placed under anything but a tentative name. It 

 has been placed by early authors under Fries' genus, 

 Diplodia. Howard mentions that a fungus probably 

 identical has been found on sugar-cane, and identified it by 

 cross cultivations with that growing on cacao (Annals of 

 Botany, vol. xv.. No. Ix., Dec. 1901). A. E. CoUens 

 reports it on the grape-vine, and Diplodia maydis on maize 

 in Trinidad (Bulletin Agricultural Department, 1909). 

 Stockdale, in the West Indian Bulletin, vol. ix., states 

 that " the ' Brown Rot ' of the cacao pod is caused by 

 Diplodia cacaoicola, the same fungus that causes the 

 ' Die-back * disease of the stem," and is in general agreement 

 with Howard's previous description. Stockdale and 

 Howard both record the exudation of spores, Howard 

 stating that " they are expelled in the form of white 

 powdery dust," and Stockdale that " small pustules may 

 be seen bursting through the rind of the pods emitting 

 a greyish white powder." Recent experiments in Trinidad 

 have shown, however, that the spores are usually expelled 

 in the form of a spiral thread consisting of the hyaline 

 spores held together by mucilaginous material, which 

 remains while they retain the hyaline form, but disappears 



