Witson: NorrH AMERICAN PERONOSPORALES 395 
This species has an interesting history, and, while known for 
some years, it has never been fully described. That it is abundant 
in those localities where it occurs is evidenced not only by the 
quotation below, but by the additional fact that in three instances 
material has been collected in sufficient quantity for distribution in 
exsiccati. The original collection was distributed in North Ameri- 
can Fungi 2207, where it received its first name. A description 
- was drawn at the same time by Dr. Halsted, to whom the material 
was submitted for determination, but .this is still unpublished. 
Swingle’s note on the species forms the basis of the diagnosis in 
Saccardo’s Sylloge Fungorum and is as follows : 
‘“‘This species has not yet been published, but seems to be a 
Plasmopara allied to P. entospora, from which it differs in having 
shorter fasciculate conidiophores and almost sessile conidia, which 
are smaller than in some forms of P. entospora. It is a very 
abundant and curious species, as yet little understood.” 
In addition to these points of difference attention should be 
called to the more globular conidia, the darker odspores with their 
less conspiciously ridged epispore, and the larger infested area with 
more pronounced discoloration of the host in the present species 
than in the former. 
On AMBROSIACEAE : 
lva xanthiifolia Nutt., Kansas, *Bartholomew (Fungi 
Columb. z&gr), *Kellerman (N. Am. Fungi 2207); 
Nebraska, *Pammel, *Sheldon; North Dakota, *Sea- 
ver; South Dakota, *Grifiths (W. Am. Fungi 797) ; 
Wyoming, *Pammel & Stanton. 
Type Ltocatity: Manhattan, Kan., on /va xanthiifolia Nutt. 
Distrisution: North Dakota and Wyoming to Kansas. 
Icon: Freeman, Minn. Pl. Diseases 111. f 45. 
3. SCLEROSPORA Schroter; de Bary, Bot. Zeit. 
390: 621. 1881 
Peronospora § Sclerospora Schroter, Hedwigia 18: 86. 1879. 
Mycelium much branched, with small vesicular haustoria ; coni- 
diophores erect, solitary or in groups of 2-3, fugaceous, low an 
Stocky, sparsely branched, the branches also stocky; conidia 
elliptic or globose-elliptic, hyaline, smooth ; oospores intramycelial, 
