ioo PLANT DISEASES 



the season minute black ascigerous fruit appears; each 

 perithecium contains a single ascus, and near its apex 

 bears a cluster of almost erect appendages, with much- 

 branched tips. 



If the fungus attacks full-grown leaves, but little injury is 

 done ; whereas when quite young leaves and tender shoots 

 are attacked, the injury is often severe. 



PREVENTIVE MEANS. Spraying with potassium sul- 

 phide, if commenced sufficiently early, checks the disease. 

 If the disease is allowed to run its course, the fallen leaves 

 should be gathered and burned, otherwise the ascigerous 

 fruit on the leaves will inoculate the trees the following 

 season. 



Galloway, U.S. Dept. Agric. Ann. Rep., 1888, p. 352, 

 pi. vii. 



SOOTY MOULD OF ORANGE 



(Meliola Various Species.) 



The black incrustation covering the leaves, and some- 

 times also the fruit, is probably met with wherever the 

 orange is cultivated. The mycelium forms a black, com- 

 pact membrane on the upper surface of the leaves, which 

 not unfrequently cracks and peels off in patches. The 

 fungus is not parasitic, but appears to assimilate the 

 ' honey-dew ' secreted by aphides and other insects, which 

 it almost invariably follows ; hence, if the trees are kept 

 free from such insects, sooty mould could not exist. The 

 fungus causes injury by preventing the leaves from per- 

 forming their functions; fruit covered by the fungus is 

 also materially injured, and often rendered unsaleable. 



