BOTANICAL GAZETTE. 327 



Enumeration of the Peronosporese of the United States. 



BY W . G . PARLOW. 



(Continued from p. 315.) 



C. Effusa. Wall of oogonium thin, corrugated at maturity. Exospore 

 thick, with a few irregular folds, which are sometimes adherent to the wall of 

 -t he oogonium. 



15. P. effusa (Grev.) Rabh. 



Botrutis effusa Grev. F .Edin. 468. 



P. effusa Rabh. in Klotzsch Herb, Myc. no. 1880 ; De Bary 1. c. p. 112 PI. VIII. f. 7, 



XIII. f. 11 ; Bull. Buss. Inst. I. 428; 29th Rept. N. Y. Bot. 52; 30th Rept. 77; 



Cat. Pac. Fung. 29. 

 P. Chenopodii Casp. Bot. Zeit. 1854. 

 Exs. Ellis N. A. F. 213. 



Conidiophores short, stout, several times dichotomous. Co- 

 nidia broadly ellipsoid, violet colored, very variable in size, 

 :22-30,a by 19-23//, often pedicellate. Oospores 26-35//. in diam- 

 eter, exospore dark brown, irregularly ridged. 



Var. major. Tips thick, short, subulate, reflexed. Conidia 

 ellipsoid, distinctly pedicellate. 



Var. minor. Narrow, lower divisions suberect, tips subu- 

 late, erect, slightly curved Conidia globose-ovoid, not distinct- 

 ly pedicellate. 



On Chenopodium, album, Atriplex hastaia; and Spinacia okracea. 



Mass. to Iowa, Wisconsin and California. Europe. 



A coarse, common species, forming a dirty white or cinereous felt on the 

 under side of the leaves of Chenopodium album and other species during the 

 whole season. We have both forms mentioned by De Bary, but with us the 

 slender form occurs on Chenopodium, and I have seen the stouter form on Atri- 

 plex. Oospores are abundant on Chenopodium, but I have not yet seen them on 

 Atriplex. 



Note.— The following three forms are very closely related to P. effusa, and 

 it is scarcely possible to state any distinct points of specific difference. As they 

 occur on hosts belonging to other orders than Chenopodiaceas, they have received 

 distinct specific names, under which they are enumerated below. 



16. P. Polygoni Thuemen, in Verhandl. Zool. Bot. Gesell. 

 Vienna, 1374. 



Conidiophores more slender, tips shorter and straighter than 

 in typical P. effusa. Conidia violet colored, without pedicels. 

 Oospores as in P. effusa. 



On Polygonum dumetorum var. scandens, Kentucky (comm. Ellis), Iowa (Ar- 

 thur). Europe. 



Forming small and rather inconspicuous patches on the under side of the 

 leaves. The Kentucky specimens contain oospores, and the conidiophores are 

 precisely like those of the form on P. avicidare, of which I have examined speci- 

 mens from Herb. Thuemen. 



