176 DISEASES OF CROP-PLANTS 



Woody Excrescences 



Instances are sometimes observed in which large woody 

 nodules or rounded excrescences are produced on stems and 

 branches. In some instances at least, the habit persists through- 

 out the life of the tree, the trunk and branches of which have in 

 consequence a very distorted aspect. 



The cause of the condition is so far unknown, but as in the 

 case of " male " trees it has been kept under observation for 

 years without any sign of communication to adjacent trees having 

 appeared. 



Root Diseases 

 The principal root diseases of cacao are caused by species of 

 Rosellinia, and are described under the heading of general 

 diseases. Occasional instances of root disease are attributed to 

 Diplodia (see Dieback). At least one other form of root disease 

 has been seen in Trinidad, but not yet investigated. 



Algal Disease 



Thread Blight 



Horsehair Blight 



Pink Disease 



{See under General Diseases). 



