228 PLANT DISEASES 



usual in the genus, often elongated when growing on the 

 leaf-sheath, whereas on the leaf the spots are usually 

 arranged in circular groups. The sori remain for a long 

 time covered by the epidermis of the leaf, which is finally 

 ruptured, exposing the conspicuous black spore-masses. 

 Teleutospores are alone known, and these remain dormant 

 during the winter, germinating the following spring. 



Preventive Means. — A portion of the plants sprayed 

 with a deep rose-coloured solution of potassium perman- 

 ganate (=Condy's Fluid) just when the leaves appeared 

 above the soil, and twice later, at intervals of ten days, 

 remained free from disease, adjoining unsprayed plants 

 being badly infected. 



Diseased leaves should not be allowed to rot on the 

 ground ; and if the plants become diseased, it is advisable 

 to remove the bulbs to some locality where the soil is not 

 infected with teleutospores. 



BEET RUST 



{Uromyces betae, Kiihn.) 



The leaves of beetroot and mangold are often infested 

 with rust to such an extent that the value of the crop is very 

 considerably reduced. The cluster-cup or aecidium stage 

 is the first to show itself ; the cups have whitish, torn edges, 

 and occur in groups on yellowish spots. These are followed 

 in June by the uredo stage. Finally, the crowded, blackish- 

 brown pustules of teleutospores follow in August, and con- 

 tinue to develop until the leaves fade in the autumn. 



Preventive Means. — Spraying early in the season with 

 dilute Bordeaux mixture or solution of potassium sulphide 

 will arrest the spread of the disease. 



The usual difficulties attend an attempt to avoid a re- 



