DISEASES OF CACAO 171 



infected cushions ; (2) in which there is hypertrophy of the pod 

 itself, producing humps or other malformations ; such pods 

 never ripen, but drop as a rule before they are half-grown ; 

 these arise from the infection of young pods ; (3) in which black 

 blotches appear on pods beginning to mature, which have been 

 previously unaffected ; the damage consequent on these spots 

 varies according to humidity ; there is a tendency for the affected 

 beans to degenerate into a mucilaginous mass, in which the 

 remainder may begin to germinate ; the apparently sound 

 beans obtained from such blackened pods are light and not 

 fully ripe. 



Effects of the Disease. 



It does not appear that the direct effects of the development 

 of witch-brooms are particularly severe. Each, of course, 

 involves the loss of a shoot, and in the extreme cases in which 

 the tree is infested with the growths this results in partial de- 

 foliation. Wlien cut back, however, the trees exhibit consider- 

 able vigour in the production of new growth. The dead witch- 

 brooms are liable to become infested with Diplodia, which then 

 gains access to the branches. Canker-like diseased areas fre- 

 quently form where they have been attached. From one cause 

 or another many trees do succumb, and supplies are generally 

 quickly attacked and prevented from developing. 



The cause of diminished production is mainly to be sought in 

 the infection of the flower cushions and the fruits. 



Causative Fungus. 



The fungus has been described by Stahel as a new species 

 under the name Marasmius perniciosus, as follows : — 



Mycelium intercellular on the living plant ; entering the cells and 

 forming abundant clamp-connections oniy in dead tissue ; when externally 

 developed turns lemon-yellow in a few days and later may show dark 

 crimson patches. 



Fructifications on their first appearance spherical, somewhat pointed. 

 Cap successively bell -shaped, fiat parasol-shaped, and frequently, when 

 old, concave above ; av. diam. 5-15 mm., max. 25 mm., thin, somewhat 

 fleshy. Primary gills 8-20 in number (avar. 15), corresponding with furrows 

 on the upper surface, 1-15 mm. wide and about 0.2 mm. thick. Upper 

 surface of cap tinted crimson, usually only faintly, with a dark-red central 

 spot surrounded by rays of the same colour. 



Stalk white to lemon-yellow according to age, hollow, 5—10 mm. in 

 length ; base swollen, mealy or scaly, light lemon-yellow changing to dark 

 brown or brownish red ; arising from a hyphal mass, not from rhizomorphic 

 strands. 



Spores 4-5 X 10-11 mic, pure white in mass ; germinate in rain water 

 after 30-40 minutes ; killed by one hour's desiccation (if spread out in 

 a thin layer). 



Occurs in damp weather on hypertrophied shoots and indurated pods 

 of cacao in Surinam. 



