174 DISEASES OF CROP-PLANTS 



ally increase in size up to diameters of 2-4 cm. In the centre of 

 the spot the mycelium occurs in the form of a very white, almost 

 shining network, and sooner or later there appear a large number 

 of slender vertical black stalks about a millimetre in height, each 

 terminating in a minute white pearl-like head of spores. 



When a pod so attacked is cut open an appearance of dry-rot 

 is seen, and such pods are always lighter than normal. Occas 

 ionally the seeds germinate inside the pod. The appearance of 

 the spots within the tissues is very dark, and not striped or 

 marbled as in the case of Monilia attack. The damage is much 

 less than is caused by the disease mentioned, not all of the seeds 

 are affected, and owing to the late appearance of the spots it is 

 possible to save the pods by timely reaping. 



Bark Rot. 



Examples of the bark infection are stated to exist on almost 

 aU the cacao trees in Ecuador. The results are much less serious 

 on the Nacional variety than on the Venezuela, of which thousands 

 of trees are said to have been destroyed. The fungus is unable to 

 attack unwounded bark, unless it be that of a tender twig or 

 shoot, but occurs in practically every cutlass wound made. 



The external surface of the bark around the cut becomes 

 discoloured, and if the weather is damp a dark wine-coloured 

 liquid may be observed to drip from the wound. Exposure of 

 the interior tissues shows a yellowish or reddish discoloration 

 which frequently extends some distance above and below the 

 wound and occasionally around the branch. Ajdark line separ- 

 ates the healthy tissues from those attacked. '^-^ ^f. 



The Fungus. 



The fungus which has been proved by numerous inoculations 

 from pure cultures to be the cause of these affections is a species 

 of Sphseronema probably as yet undescribed. The black stalks 

 mentioned above are the slender elongated necks of buried 

 pycnidia, producing pycnospores ; the white mycelium on the 

 spots forms conidia in simple chains, and chlamydospores are 

 produced on the hyphae. 



Anthracnose 

 At least one definite anthracnose of cacao pods occurs in the 

 West Indies, existing quite apart from other types of pod dis- 

 eases. Little importance has been attached to it, and it has not 

 been made the subject of any detailed investigation. 



Symptoms. 



With the following description by F. W. South, later observa- 

 tions, made by the writer in St. Vincent, agree. " Infection 

 usually shows itself in the form of small spots on the surfaces 



