DISEASES CAUSED BY FUNGI 33 



among the best authorities. Sooty moulds are not uncommon in 

 temperate countries and have there been usually placed in the 

 genus Capnodium, while those of the tropics were regarded as 

 species of Meliola until they were excluded by Gaillard in 1892 

 as non-typical of that genus. With this exclusion F. L. Stevens, 

 who has recently studied in detail the true Meliolas of Porto 

 Rico, entirely agrees, but he leaves open the question of their 

 correct position, save for the conclusion that in the main they 

 belong to the Capnodiae of Saccardo. Possibly the genus Fumago, 

 an older name than Capnodium, should be revived to contain 

 them. 



The Meliolas proper appear as black blotches on leaves, 

 made up of a network of hyphae closely set with short branch-like 

 appendages, and bearing various reproductive bodies. They 

 appear to exhibit specialisation on particular plants or related 

 groups much in the same way as the Erysiphaceae and are probably 

 parasitic, though producing as a rule very little visible effect 

 on their hosts. 



The sooty moulds, on the other hand, show no specialisation 

 and no sign of parasitism. They occur most frequently in 

 association with infestations of scale insects, aphides, white 

 flies, and the more sedentary species or stages of leaf-hoppers 

 (Fulgoridae, Membracidae, Jassidse), developing wherever the 

 sweet secretions of these insects (honey-dew) are sprayed by the 

 insect or spread by dew or rain, whether the situation be the 

 leaves and bark of the infested plant and its neighbours, or 

 even soil or stones. They will similarly appear and spread in 

 the nectariferous spray or washings from some profusely flowering 

 trees, and it is said that spraying a tree with a sugary solution 

 will produce a heavy infestation. 



The injury to the plant due to prevalence of sooty moulds 

 arises from the film which covers the leaves, reducing the access 

 of light and obstructing the exchange of air and water vapour. 

 There is also some commercial loss from the disfigurement of 

 fruit. The degree of these effects naturally depends on the 

 amount and duration of the fungus, and this again on the con- 

 tinued prevalence of the insect which supplies its nourishment. 

 The effects of the insect, which is frequently obscure, are usually 

 mistaken for those of the fungus, which is prominent, and the 

 latter are consequently greatly exaggerated. Black blight, 

 in fact, is the great bugbear of the West Indian planter and 

 gardener, and it is to be regretted that some of the attention it 

 receives is not transferred to the many matters more deserving 

 of his solicitude. 



It is not denied that long-continued infestation may have a 

 debilitating effect on a tree, and reduce its production of fruit, 

 but attention should be directed, not to the fungus, but to the 

 primary pest. The belief which exists that black blight is 

 contagious is true only in the very limited sense that plants 



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