486 DISEASES OF CULTIVATED PLANTS 



placed it over a young vegetable marrow plant growing under 

 glass, and within three days every leaf was destroyed by the 

 disease. 



Minute, pale green, translucent spots first appear on the 

 leaves, which rapidly increase in size and run into each other 

 and turn brown. This may all happen within twenty-four 

 hours. The foliage as a rule is killed so rapidly that the 

 plants become waterlogged and die, due to continued activity 

 of the roots. Conidia appear in numbers when the spots 

 turn brown, and these are distributed by spraying, etc. 

 Conidia that fall to the ground germinate quickly, and form 

 mycelium which soon produces more conidia. The mycelium 

 continues to grow in the soil for at least a year, and pro- 

 duces crop after crop of conidia. 



The fungus is Cercospora melonis (Cke.), 



The conidia are large, cylindrical, and narrowed towards 

 the tip, 7-9 septate, 80 X 9 /A, supported on dark coloured, long, 

 slender, simple or branched conidiophores. 



Soft foliage favours the disease, which does not occur on 

 plants not grown under rushed conditions. Even badly 

 diseased plants, when planted in the open air, produce new 

 leaves and continue healthy. Spraying with sulphide of 

 potassium, if begun as soon as the disease appears, 

 retards its progress. The soil should also be thoroughly well 

 soaked with the solution. Diseased plants should be removed 

 and burned. Care should be taken not to introduce the 

 disease by any of the means cited above. The disease is not 

 carried in the seed. 



Massee, Journ. Board Agric.^ Leaflet No. 76. 



Celery and parsnip leaf blight. Somewhat early in the 

 season, more especially during dull, damp, warm weather, 

 the parasitic fungus known as Cercospora apii (Fr.), often 

 causes serious injury to celery and parsnip leaves. The 

 outermost leaves first show the disease under the form of 

 roundish blotches of a sickly green colour at first, gradually 

 changing through brown to grey when old. As the disease 

 progresses the leaves turn yellow and wilt ; at this stage the 

 fruit of the fungus, which emerges through the stomata in 

 tufts, is produced, and the spores are washed by rain or 

 conveyed by other agents to other leaves which become 

 infected, and in turn produce a crop of spores. I have 



