Witson: NortH AMERICAN PERONOSPORALES 403 
On BALSAMINACEAE : 
Impatiens aurea Muhl., Alabama, Earle & Underwood ; 
Indiana, Arthur ; lowa, Holway. 
Impatiens biflora Walt., Connecticut, Underwood 2981 ; 
Delaware, Commons (type of Peronospora Jmpatientis 
Ellis & Everh.) Jackson 1572; District of Columbia, 
Williams ; Indiana, Olive, Underwood, Wilson ; Mass- 
achusetts, Farlow, Halsted & Farlow (N. Am. Fungi 
207), Seymour (Econ. Fungi Aza, on ‘‘ /mpatiens 
sp.’’), Zrelease ; Michigan, Merrow (Econ. Fungi A47#, 
on ‘ /mpatiens sp.’); New York, Dudley & Under- 
wood ; Wisconsin, Davis, Pammel. 
Impatiens sp., West Virginia, Sheldon. 
TYPE Loca.ity : Rastatt, Germany, on /mpatiens Nolitangere L. 
DistRIBUTION : Vermont to Minnesota, southward to Alabama. 
Also in Europe. 
Icon: Berlese, Icon. Fung. Phye. f/. 75. 
6. Rhysotheca Halstedii (F arl.) 
Peronospora Halstedii Farl.; Ellis, N. Am. Fungi 209. 1879. 
(Hyponym); Proc. Am. Acad. 18:72. 1883. 
Peronospora Halstedii Ambrosiae Ellis, N. Am. Fungi 270. 1879. 
(Hyponym. 
Plasmopara Halstedii Berl. & De-Toni, in Sacc. Syll. Fung. 7 : 242. 
1888. 
Hypophyllous, on cotyledons and leaves, the affected area 
small, 1-3 mm., or extending over the entire leaf; conidiophores 
fasciculate, slender, 300-750 4, 3-5 times branched, ultimate 
branchlets 8—15 » long, verticillate below the apex of the branch- 
Ing axis which is frequently swollen and ganglion-like ; conidia 
Oval or elliptic, 18-30 x 14-25 #; OOspores 30-32 /4; epispore 
yellowish-brown, somewhat wrinkled. 
This is the most unsatisfactory species of a difficult genus. 
The conidiophores are very variable, especially in the laxity of their 
branches and the development of the ganglion-like swelling from 
Which the ultimate branchlets arise. Several forms are clearly 
distinguishable and are apparently valid species, but further search 
has invariably brought to light intermediate forms connecting the 
_ €xtremes with the typical form and with other forms. Until an 
