1 







ON THE OCCURRENCE OF PERONOSPORA PARASITICA ON 



CAULIFLOWER. 



BY HERMANN VON SCHRENK. 



were 



During the winter months of 1903 the cauliflower plants 

 in a greenhouse of the Missouri Botanical Garden 

 universally attacked by the crucifer mildew (Peronospora 

 parasitica, De Bary). The fungus made its appearance 

 very suddenly, and within a week had spread over practic- 

 ally all of the plants in the affected greenhouse, attacking 

 both the old and the young leaves. So virulent was the 

 attack that it looked for a time as if the whole crop would 

 be destroyed. So far as one could determine, this was the 

 first appearance of this mildew on the cauliflower, at least 



for a long 



period of years 



in the greenhouses of the 



Missouri Botanical Garden, and probably in the western 

 States. 



The crucifer mildew is one of the most widespread of all 



mildews 



r> 



cruciferous plants. It is extremely common on many of 

 the wild Cruciferae, appearing generally early in the sprino-. 

 Cardamine hirsuta and C. laciniata are particularly sub- 

 ject to it, and, of cultivated plants, radishes and cabbages 

 are frequently attacked by this fungus. Halsted* 

 one of the first to call attention to its occurrence on culti- 



was 



vated plants, particularly on radishes and cabbage. 



He 



Aly, 



iritirnum f and n 

 IZaphanus and B 



* Halsted, B. D., Twelfth Annual Report, New Jfersey Agricultural 

 Experiment Station, page 248. (1892). 



t Halsted, B. D., 13th Annual Report, N. J. Agr. Experiment Station, 



page 277. (1893). 



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