Studies on the Downy Mildew op Onions 5 



originally published by Unger. Farlow (1884) suggested that the 

 change was made on etymological grounds, while Gaumann (1923) said 

 that it probably was an error on the part of de Bary. 



Peronospora alliorum is the name under which this fungus was dis- 

 tributed by Fuckel in 1863 in Fungi rhenani exsiccati no. 41. Later 

 Fuckel (1869) accepted the name given by de Bary and placed Peronos- 

 pora alliorum in synonymy under Peronospora schleideniana. 



As a result of de Bary's influence the fungus was known under the 

 name of Peronospora schleideniana for many years, but recently Per- 

 onospora schleideni has been used more commonly. 



Wilson (1914) discussed the synonymy of this fungus briefly, and 

 considered Peronospora destructor (Berk.) Caspary the correct name. 

 Gaumann (1923), however, disagreed with Wilson on this point, and 

 insisted that the correct name is Peronospora schleideni Unger, since 

 this antedates Peronospora destructor by thirteen years. 



Gaumann was correct as far as the dates of publication of the bi- 

 nomials are concerned, but he evidently overlooked the fact that the 

 species name "destructor" antedates "schleideni" by six years, and 

 that the perfect stage is included in the description of Peronospora 

 destructor while only the conidial stage is described for Peronospora 

 schleideni. 



The writer concludes that the valid name of the causal organism of 

 downy mildew of onions is Peronospora destructor (Berkeley) Caspary, 

 with synonymy as follows : 



Botrytis destructor Berkeley, Ann. and Mag. Nat. Hist. 6:430. 1841. 

 Peronospora schleideni Unger, Bot. Ztg. 5:315. 1847. 



]'< ronospora schleideniana (Unger) <le Bary, Ann. Sci. Nat. 4:20:122. 1803. 

 Peronospora alliorum Fuckel, Fung. rhen. n. 41. 1803. 



DISTRIBUTION 



Downy mildew is present, and often destructive, on onions of various 

 kinds in nearly all parts of the world. It is known to occur in Bermuda, 

 the Canary Islands, China, Denmark, England, France, Germany, 

 Holland, Ireland, Italy, Japan, Mauritius, New Zealand, Norway, 

 Russia, Spain, the United States, and Western Australia. In the 

 United States it has been reported in the Plant Disease Reporter (1917 

 to 1930) from the following States: Arkansas, California, Colorado, 

 Connecticut, Georgia, Kentucky, Louisiana, Maine, Maryland, Massa- 

 chusetts, Michigan, Minnesota, Mississippi, Missouri, New York, North 

 Dakota, Ohio, Oregon, Pennsylvania, Vermont, Washington, West Vir- 

 ginia, and Wisconsin. The geographical distribution of the disease in 

 this country, and the number of times that it has been reported from 



