ee 
4 
: 
Witsox: NortTH AMERICAN PERONOSPORALES 399 
genus cannot stand under the present tribe. That the method of 
germination is more nearly analogous to that of the Peronosporeae 
isthe view held by the present author. The genus Rhysotheca is 
therefore the most highly developed and the typical genus of the 
group of genera the conidia of which germinates by zodspores, while 
Plasmopara stands in the same relation to Peronospora as does 
Pseudoperonospora to Rhysotheca. 
Key to the species 
Conidiophores low, averaging 300 yw or less, 2-3 times 
bra 
nched, the branches short. . R. Geranit. 
Conidophores | tall, averaging over 300, 2-5, usually 4 
or 5, times branched, the branches desig: 
Ultimate branchlets elongate, cylind 
rimary branches short, keels tase 2. R. Umbelliferarum. 
oneal branches elongate, lax 
Conidiophores 3-4 ‘ise ieanchok: 
Conidia small, about 15 & I7 1. 3X. 
Conidia large, about 27 X 35 #. 4. R. A loca 
Conidiophores 4-5 times branched, very lax. 5. &. 
Ultimate branchlets more or less conic. 
U 
econdary branchlets very short. 6. R. Halstedii. 
Secondary branchlets lax 
Secondary branchlets sparingly branched. 
ee 
bout 12 15 yu. 7. &. australis. 
Conidia about 15 & 18 yu. 8: R. illinoensts. 
cies branchlets much branched ; 
onidia about 14 < 22 g. R. viticola. 
Ultimate events ts narrowly (oases 
Conidia elliptic, about 15-20 long. 
Conidiophores 2-4 times branched. 10, R. Viburni. 
Conidiophores 3-5 times branched. 11. &, ribicola. 
Conidia globose-elliptic, about 18-304 long. 12. X, Gon olobt. 
1. Rhysotheca Geranii (Peck) 
Peronospora Geranii Peck, Rep. N. Y. State Mus. Nat. Hist. 28 : 63. 
1876. 
Peronospora nivea Geranti Farlow; Ellis,N. Am. Fungi 278. 1879. 
Plasmopara Geranii Berl. & De-Toni, in Sacc. Syll. Fung. 7: 248. 
1888. 
Hypophyllous ; - infected areas conspicuous, definite in outline, 
Or often covering the entire leaf, white-downy ; RE ET 
fasciculate, monopodially 2-3 times branched, the branches 
