84 CACAO 



or burning of diseased and dead parts of host plants, 

 which contain the hybernating oospores, by change of 

 crop of infected fields, and by treatment with copper re- 

 agents." 



Phytophthora is highly infectious. Once a cacao pod 

 is infected, the fungus permeates the pod by means of the 

 slender fungus filaments called hyphce and, protruding 

 through, appears upon the surface in the form of white 

 mould. The hypha is enabled to pierce the epidermis 

 from the inside by the action of a solvent substance 

 excreted by the growing tip of the hypha, the protoplasm 

 secreting a ferment which passes out and enables the tip 

 to corrode and dissolve away the substance of the cell-walls. 

 When the hypha has protruded from the surface conidia or 

 sporangia are developed, and these sporangia again give 

 rise to swarm cells, which have the power of movement 

 in a drop of water. " When a conidium germinates in a 

 drop of dew or rain, the normal process is as follows : 

 The protoplasm in the interior of the pear-shaped conidium 

 becomes divided up into about twenty or thirty little 

 rounded masses, each of which is capable of very rapid 

 swimming movements ; then the apex of the conidium 

 bursts and let these motile zoospores, as they are called, 

 escape " (Marshall Ward, p. 280). Each zoospore then 

 swims about for a time, and at length comes to rest, 

 commences to grow in about half an hour, and then begins 

 to bore its way again into its host. 



" The whole process of germination and the entrance 

 of the fungus into the tissues up to the time when it, in 

 turn, puts out its spore-bearing hyphce again, only occupies 

 four days during the moist warm weather in May, June, 

 and July " (Marshall Ward). It is probable, therefore, 

 that under the conditions of heat and moisture which 

 exist in Trinidad, the organism will have still more rapid 

 growth than in a temperate climate. The average size of 

 a conidium, according to the above author, is ^J^ in. long 

 by Y^ in. broad, and the zoospores have a diameter of 

 about Y^ in. 



