172 
Journal oj Mycology 
[Vol. 10 
A point to be emphasized is the distant location in systematic 
classification of the hosts of Peronospora parasitica and that of 
the parasite of Floerkea. Were there a close affinity between 
the plants attacked by these Mildews, the marked morphological 
similarity of the latter could well be interpreted as indicating a 
close genetic relationship. They might in such a case be, with 
some degree of propriety, recorded as biological species with as 
yet slightly perceptable morphological differentiation. But the 
facts noted seem to warrant the conclusion that we have to do 
with an unnamed but valid species, and consequently the name 
Peronospora Hoerkeae is proposed. 
Unfortunately the germination of the conidia was not wit¬ 
nessed. Repeated efforts to determine whether a germ tube pro¬ 
ceeded from the conidium, or whether this formed zoospores, 
were unsuccessful. In one or two cases a structure was seen on 
the slide that was with some hesitation taken to be the germ tube 
and in multitudes of conidia observed no indication of zoospore 
formation was detected. Consequently the fungus is referred 
to the genus Peronospora rather than Plasmopara. If however 
an error has been made here the plant would bear the name of 
Plasmopara floerkeae. The following diagnosis is offered. 
Peronospora floerkeae Kellerm. n. sp.— Conidiophores 
stout (16-18/x wide) simple below and elongated, irregularly and 
profusely branching above, the branches again subdividing some¬ 
times dichotomously but oftener irregularly, the ultimate branch- 
lets more or less plainly dichotomous also much elongated and 
strongly curved; the branches are very much narrower than the 
main axis of the conidiophore, the ultimate branches being very 
narrow and bearing large hyaline oval or sub-globose conidia 24- 
32 x 18-25 fi; germination unknown. Oospores numerous, sub- 
globular, 24-36 n f the wall light brown and smooth or slightly 
rugose. 
On Floerkea proserpinacoides Willd.; Columbus, Ohio. 
May 1902 and 1904. 
Strongly resembles Peronospora parasitica (Pers.) Tul. but 
more irregularly branching, the ultimate branchlets longer, usu¬ 
ally dwarfing but not otherwise deforming the host which does 
not belong to Cruciferae (as do all the hosts of Peronospora 
parasitica) nor to a closely related family. 
EXPLANATION OF PLATE 74. 
Fig. 1. Floerkea proserpinacoides dwarfed by Peronospora 
floerkeae which infests it throughout. Figs. 2, 3, 4. Conidio¬ 
phores of Peronospora floerkeae. Fig. 5. Four conidia. Fig. 
6. Two oospores. 
