PERONOSPORALES 2 1 9 



diagnosis, and the reader is left in some doubt as to the essential 

 characters of the genus. Article 38 of the International Rules of 

 Botanical Nomenclature requires that a diagnosis accompany 

 a new name in publication Since Rostowzew made no reference 

 to the subgeneric diagnosis of Berlese he may be assumed to have 

 been ignorant of its existence, and consequently article 49 of the 

 Rules relating to the elevation of a subgenus to generic rank does 

 not apply (see Curzi, 1926). In 1905 CUnton, reaUzing this 

 situation and feeling that Pseudoperonospora would not stand, 

 raised the subgeneric name Peronoplasmopara Berlese to generic 

 rank and pubhshed a generic diagnosis. CUnton (1905 a: 334) 

 discusses the situation at length, and the writer agrees with his 

 conclusions. The name Pero7ioplasmopara, attributed by CUnton 

 to Berlese, is, therefore, applied. 



Since the erection of the genus on the two above named species, 

 several others have been incorporated. These include P. humuli 

 Miyake & Tak., the hop mildew, and P. canahina (Otth) 

 PegUon, the mildew of hemp. A recently described species, 

 P. porioricensis Lamkey (see Stevens, 1920) differs in that the 

 sporangia are small and hyaline. It is not unlikely that the 

 limits of the genus will be stiU further altered to include other 

 species. Clinton has already pointed out that a critical study 

 of all the species of Plasmopara and Peronospora may show 

 that these genera grade into each other through so many forms 

 that the attempt to recognize an intermediate genus such as 

 Peronoplasmopara will only add to the difficulty of maintaining 

 generic separations. Nevertheless, at present, recognition of the 

 genus seems justified. 



5. Bremia Regel (1843). 



Mycelium intercellular, sending unbranched clavate to globose 

 haustoria into the host cells; sporangiophores protruding from 

 the stomates, where two or three have a common origin in a 

 bulbous swelling of a single hypha; branching definitely dicho- 

 tomous; each terminal branchlet broadened at its tip to form a 

 shallow saucer-shaped disc from the edges of which several short 

 sterigmata arise each bearing a sporangium; sporangium hyaline, 

 with an apical papilla through which a germ tube is usually 

 protruded. 



Rarely germination is by swarmspores (Milbrath, 1923). The 

 best known species B. lactucae Regel (Fig. 79) occurs on lettuce 



