CERCOSPORA 



487 



proved by inoculation experiments that when the spores are 

 placed on a young celery leaf, a disease spot becomes evident 

 about the fourth day, and that mature spores are produced in 

 four weeks. 



The pale olive sporophores originate from colourless 

 mycelium in the tissue of the leaf, and come to the surface 

 of the leaf in clusters through the stomata of the leaf. Spores 



Fig. 147. Cercospora apii. 1, celery leaf attacked by 

 the fungus ; 2, fruit of fungus, highly mag. 



hyaline, almost cylindrical, a little thickened at one end, 3-10 

 septate, 50-80 x 4 /x. 



Spraying with ammoniacal carbonate of copper solution is 

 most efficient in checking the disease, if applied before the 

 disease has advanced too far. The spores on diseased leaves 

 live through the winter, and are capable of infecting a crop 

 the following season, hence the leaves should be gathered and 

 burned. Some portions of leaves, however, are certain to 

 remain on the ground, and rotation of crops, where practic- 

 able, would be the safest method. It is stated that when 

 celery is shaded by some means it remains free from disease. 

 This method, however, is only practicable perhaps on a 

 small scale. 



