DISEASES OF CITRUS TREES j 



and it is not yet settled whether they are saprophytes 

 or really parasites. Probably they partake of the nature 

 of both. They may commence as saprophytes feeding 

 on the thin layer of dead wood over the surface of the 

 wound. After some time the poison which they develop 

 destroys the healthy wood, and death travels down the 

 trunk, the fungus keeping equal pace with it, killing 

 first the duramen and then the soft alburnum. Canker 

 alone will kill the tree after many years, but generally 

 gummosis surpervenes arid death ensues in a few months. 

 Exposure to rain-water causes the canker to take a 

 more acute form. To avoid this many cultivators cover 

 the cankered wound with cork, and fill the interstices 

 between this and the bark with a mixture of equal parts 

 of resin, bees wax, tar and powdered clay, melted 

 together over a fire. Others perforate the trunk at a 

 level with the bottom of the cavity produced by canker, 

 so as to prevent the accumulation of rain-water. 



The sooty mould of the Citrus trees, Meliola Penztgi, 

 Sacc., or Capnodium Citri, Berk., (Fumago vagans) ap- 

 pears early in autumn as small black spots upon the leaves, 

 and gradually develops into a sooty crust covering the 

 upper surface of the leaves, the fruit, and the green bark 

 of the twigs. The black mass consists of bottle- shaped 

 conidiophores imbedded in a thick mycelium. This fungus 

 and its congener the Meliola Citri, Sacc., arjpear with 

 great activity on those trees which are suffering from a 

 bad attack of scale insects. These insects exude a thick 

 sugary juice which sometimes besmears the upper surface 

 of the leaves and fruit (called melata by Italian writers), 

 and offers a suitable ground for the growth of the sooty 

 mould. Want of proper ventilation, the vicinity of high 

 walls, and the presence of exuberant foliage favour an 

 attack of the sooty mould. A Citrus tree attacked by this 

 fungus assumes a gloomy aspect, only partly relieved 

 by the few green leaves which have escaped infection, 

 and the unsightly fruit is sold with difficulty or fetches 



