398 Witson: NortH AMERICAN PERONOSPORALES 
of the host. That these species are members of the present order 
is doubtful ; and if they are, it is still more improbable that they 
are congeneric with the American species. 
S. Magnusiana Sorokin, Rev. Myc. 11: 143. 1889. On 
Equisetum sp., in the region of the southern Ural Mountains of 
Russia. 
S. macrospora Sacc. Hedwigia 29: 155. 1890. On Alopecu- 
rus sp. in Australia, and Triticum vulgare L., in Europe. 
S. Kriegeriana Magnus, Verh. Deutsch. Naturf. 67: 100. 
1895. On Phalaris arundinacea L., in Europe. 
4. RHYSOTHECA gen. nov. 
Peronospora § Zoosporatoparae de Bary, Ann. Sci. Nat. IV. 20: 
105. 1863. 
Mycelium branching ; haustoria simple ; condiophores erect, 
solitary or fasciculate, projecting through the stomata of the host, 
monopodially branched, the branches usually arising at right angles 
to the main axis, as do also the secondary branches, at least never 
appearing truly dichotomous, the ultimate branches apically ob- 
oogonium 
persistent but free from the odspore. (Etymology, Juadc, wrinkled, 
Gijxn, casket.) 
Type species, Peronospora witicola (B. & C.) Casp. 
To this genus belong the greater number of species which are 
usually referred to Plasmopara. That they are closely related to 
the preceding genera is evidenced by the habit of branching of the 
conidiophores and the germination of the conidia by zoospores. 
Plasmopara, sensu stricto, has conidiophores with the ultimate 
branchlets apically obtuse as in the present genus, but with the gen- 
eral method of branching more nearly dichotomous than mono- 
podial, and with the conidia germinating in a decidedly anomolous 
manner. The membrane breaks as in the present genus and the 
entire protoplasmic content €scapes in a mass, forming a non- 
motile plasma from which a germ-tube is produced. That this is 
not the typical method of germination either for the Rhysotheceae 
or the Peronosporeae is evident, and unless the formation of a 
plasma be construed as the equivalent of zoospore-formation the 
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