66 KANSAS Academy of Science. 



ANALYTICAL KEY TO THE GENERA. 



A) Conidiophores short, produced inside of the host. Conidia catenulate. 

 1. Cystopus. Conidia and oospores producing zoospores. 



B) Conidiophores arising from the host through fissures. Conidia solilary. 



■f Conidiophores sparingly branched, at first producing conidia acrogenously, 

 then also on the sides. 

 Phytophthora. Conidia jiroducing zoospores. 

 "I"! Conidia always acrogenous. 



§ Conidiophores with rather short, obtuse terminal branches. Conidia never 

 germinating directly, but by zoospores or by discharging the whole pro- 

 toplasm. 

 Sclerospora. Wall of oospore thick. Germination by zoospores. 

 Plasmopara. Wall of oospore thin. Conidia producing zoospores or discharging 

 (before germination) the whole protoplasm. 

 H Conidiophores many times dichotomously branched, terminal branches sub- 

 ulate uncinate. Conidia germinating directly. 

 Bremia. Haustoria not branched. Conidia germinating through an apical papilla. 

 Peronospora. Haustoria branched, conidia destitute of an apical papilla, germinat- 

 ing laterally. 



CYSTOPUS Leveille, in Ann. Sci. Nat., ser. 3, t. VIII, p. 371. [Bull. Bussey Inst., vol. 

 1, p. 429, Bot. Gaz., vol. VIII, p. 334. Syll., vol. VII, p. 233.] 



Conidiophores simple, smooth, cylindrical, or clavate, very obtuse, arising as 

 branches from the mycelium and collected in large numbers in cushion-shaped 

 sori, bearing a single apical moniliform series of conidia. Sori at first covered 

 by the epidermis of the host plant, then bursting open the epidermis and scat- 

 tering the mature conidia, either white or yellowish. Conidia either all of the 

 same form, hyaline, generating zoospores, or of two forms, mostly hyaline and 

 producing zoospores, but with a few at the ends of the chains with a thicker, often 

 lutescent wall, either germinating by a simple tube or sterile. Oospores globose, 

 epispore mostly reticulate or warty. 



^ I. Exosporium thick, plainly four-layered; conidia globose or rounded quad- 

 rate (short cylindrical).* 



1. Cystopus candidus (Pers.) Lev., in Ann. Sci. Nat,, ser. 3, t. VIII, (1847) p. 371, Ubedo 

 (Albugo) oandida, Pers. Synops. Meth. Fung., p. 223. [Bull. Bussey Inst., vol. I, 

 p. 429, Bot, Gaz., vol, VIII, p, 334, Syll., vol. VII, p, 234, No. 792.] 



Conidia and oospores on leaves, stems and inflorescences of Cruciferae March 

 to August, most common April and May. 



On Draba CaroUniana Walt. 

 1512, with immature oospores, on leaves. May 1, 1888, Manhattan. {Peronospora 

 parasitica, No. 1512a, occurs on the lower leaves of the same plants.) 



On Sisymbrium canescens Nutt. 

 1580, on leaves, March 26, 1889, Manhattan; 1616, on leaves, March 29, 1889, Man- 

 hattan; 1537, on leaves, April 4, 1889, Manhattan; 1596, on leaves, April 22, 1888, 

 Manhattan; 1533, on leaves, April 25, 1889, Manhattan {Peronospora parasitica No. 

 1533a occurs on leaves and stems of the same plants); 1516, on leaves. May 4, 1885, 

 Manhattan; E. Bartholomew No. 294, on leaves, with very young oospores. May 27, 

 1889, Rooks county. 



* Zalewski Zur Kenntniss der Gattung Cystopus, Lev., in Botanisches Centralblatt, Band XV, (1883.) 



No. 7 (33), S. 222. 



