190 A Monograph of the Ervsiphaceae 



Will be found a very good remedy. The powder should be dusted 



r 



on the foliage at the first appearance of mildew and the operation 

 repeated every ten or twelve days, or more often if there is an 

 abundance of rahi. If one has a spraymg machine, a solution 

 made by dissolving 3 ounces of carbonate of copper in 2 quarts 

 of aqua ammonia diluted to 22 gallons will be found an efficient 

 remedy. This solution should be applied every twelve or fifteen 

 days, beginning at the first appearance of the disease." 



The '* mildew of turnips" is also caused by E, polygom. 

 Hitherto the fungus causing this disease has been known only in 

 its conidial stage, and has been wrongly identified as Oidunn Bal- 

 samii (Mont, mss.) Berk. & Broome. Worthington G. Smith 

 (3-9' P- 76) fii"st gave it this name, and described the disease as 

 follows : " Oidiian Balsai)iii^ Mont., first attracted attention as a 

 pest of turnips in September, iSSo, when Prof James Buckman, 

 F.L.S., of Bradford Abbas, Dorsetshire, saw the fungus grow- 

 ing in such profusion over hundreds of acres of Swede turnips 

 that the boots and clothes of persons walking through the turnip 



fields were whitened with the spores. Until 1880 the fungus was 

 not supposed to be common in Britain. . . . Important as this 

 Oiduiui is to agriculturists, no one at present has w^orked out its 

 life-history, or knows whence it comes, where it goes, what other 

 form it takes, or how it hibernates through the winter. The fun- 

 gus is more prevalent when a humid September follows on a dry 

 August." Trail (365) notices the disease, and says of ''Oidiinn 

 Balsamii'' '* It is of considerable practical interest, since it attacks 

 various cultivated plants. Near Aberdeen [Scotland] I have seen 



it in great plenty upon turnips, preferring the Swedish to the com- 

 mon yellow turnip." 



In the beginning of November, 1898, my attention was di- 

 rected to some fields of turnips, near Reigate, Surrey, England, 

 which were, in places, quite white with mildew. On examination 

 it was found that this appearance was caused by the presence of 

 an Oidiurn, which agreed with specimens in the Kew Herbarium 

 named 0. Bahamii^ on turnips, by Worthington G. Smith. 0. 

 Balsamii (Mont, mss.) is thus described by Berkeley and Broome 

 (38): "Candida, articuhs doliiformibus utrinque angustatis. On 

 the leaves of Verbasaini nigrum^ Wothorpe, Aug. 23, 1853. This 



