Yin FOREST & ORNAMENTAL TREES 253 



Nectria. Very few tropical fungi have received as 

 much attention as the species which belong to the 

 genus Nectria. At least two species (N. cinnabarina, 

 (Tode) Fr., and N. ditissima, Tul.) are widely dis- 

 tributed throughout both tropical and temperate regions. 

 They are strictly wound parasites which attack various 

 parts of the plants. 



The mycelium penetrates the tissues, living primarily 

 in the tracheary tissues of the host. The bark on the 

 part which is suffering from the attack becomes shrivelled 

 and dies. Eventually, wart-like bodies, about the size 

 of millet seed, and of a yellowish, brownish, or reddish 

 colour, are produced. On the surface of these bodies 

 are grown great numbers of the conidia spores by which 

 the fungus spreads rapidly. After a time these bodies 

 cease to produce the conidia arid become somewhat 

 firmer in texture, and bear the perfect fruit or spores of 

 the fungus. In this later condition they contain more 

 or less flask-like cavities within which are borne the 

 little sacs or asci. Each ascus contains eight 2 -celled 

 spores which are usually hyaline and elliptical. These 

 organisms are most destructive on the cacao on which 

 are recorded N. theobromae, N. cinnabarina, N. ditis- 

 sima, N. cqffeicola on the stems ; N. Bainii on the 

 pods ; and N. striatospora on both stems and pods ; 

 N. ditissima occurs on both coffee and tea. N. diversi- 

 spora and N. funtumia occur on rubber. 



Exoascus. The species of this genus attack leaves 

 (see page 42), fruits, and buds. When they attack 

 the buds they usually cause the formation of witches' 

 brooms. The most important of these witches' 

 brooms which has been reported is the one on cacao, 

 which is caused by E. theobromae (see page 183). 

 These unsightly growths should be removed and burned 

 so as to prevent the formation of spores and the spread 

 of the disease. 



Witches' Brooms are also caused by several other 

 fungi and by insects, more especially the mites. They 

 are not only injurious to trees, but are very unsightly. 



