DISEASES AND ENEMIES 249 



other, e.g. by thrips or by other insects, by winds or 

 by the witch-broom disease (Surinam). From here it 

 makes its way downward into the branches, finally 

 reaching the stem ; but sometimes it stops at the place 

 of junction of a side branch or of a main branch with 

 the stem, thus restraining its ravages to a part of the 

 branch system. 



The disease has also been known to appear in 

 perfectly strong and healthy trees after careless pruning, 

 and also after pruning in the wet season, when the rains 

 have prevented a thorough tarring of the cut surfaces. 



The disease makes its way much more quickly along 

 than across the branches, and a branch may often be 

 seen attacked over its whole length but only on one 

 side (often the underside) ; here the rind is dead, but 

 is still fresh along the other side of the branch, which 

 bears fresh green leaves. 



Very characteristic is the discoloration of the wood 

 in the diseased parts of branch and stem. It first 

 assumes a light-brown colour, and becomes greyer after 

 death owing to the black colour of the fungus threads, 

 which grow through the tissues. With the microscope 

 the mycelium is to be seen running through the tissues ; 

 when young the hyphae are colourless, when older they 

 become darker and give a greyish colour to the wood. 

 It was at first thought that the disease was caused 

 in the different countries by different though closely 

 allied fungi. In Grenada, St. Lucia, St. Vincent, and 

 Dominica a Diplodia was found ; in Trinidad a 

 Lasiodiplodia ; and in Surinam a Chaetodiplodia. 

 It has been proved, however, 1 that all these fructifications 

 belong to the same fungus, which accordingly may be 

 called Diplodia cacaoicola (Fig. 81). 



Another higher fructification of the Diplodia has 

 been found by Keith Bancroft to develop on the dead 

 wood and has been named Thyridaria tarda. As, 



1 Van Hall-de Jonge and Drost, "The Die-Back Disease," etc. (Recueil des 

 travaux botaniques n&rlandais, vol. vi. 1909) ; van Hall-de Jonge and Drost, 

 "De instervingsziekte der cacaobooinen " (Bull. No. 21 of the Dept. of Agr., 

 Surinam}. 



