144 DISEASES OF CROPS. 



the ravages of Cystopus and other parasitic fungi. (4) 

 Top-dress the land (when the plants are young) with half 

 cwt. of iron sulphate mixed with 5 to 10 times its weight 

 of sand or dry earth per acre. This dressing prevents 

 the attacks of '' white rust," and is most beneficial as a 

 plant-food. 



Cure. — Water the infested plants with a solution of 

 iron sulphate (1 to 5 per cent, solution) at the rate of 2 or 

 3 gallons per acre. 



(3) The Parasites of Celery {Apium graveolens). 



The Celery Stem Fly (Piophila apii). The larvae 

 of this dipterous fly feed within the stems and leaf-stalks 

 of celery plants. The cream-coloured larvse are devoid 

 of legs, and turn to pupse within the host-plants. The 

 thorax and abdomen of this fly are black, while the head 

 is of a brown colour. P. apii is about half an inch across 

 the extended wings, which are almost colourless. The 

 fly makes its appearance in May, and there are two broods 

 during the year. 



Prevention. — (1) Destroy infested stems. (2) Top- 

 dress the young plants with soot or a mixture of slaked 

 lime and soot. 



The Celery Leaf Miner {Tephritis onopordinis) 

 has already been described as a " parasite of parsnips." 



The Red Rust of Celery {Puccinia apii). The 

 early stage of this fungus is known as Uredo apii, or 

 " red rust" ; and the later stage as Puccinia apii, or the 

 "black mildew" of celery. The fungus is allied to, and 

 has a somewhat similar life-history to, Puccinia graminis 

 already described. 



Prevention. — (1) As Dr. M. C. Cooke proved the disease 

 to be hereditary, seeds from infested plants should not be 



