July 1904] 
A New Species of Per onosp or a 
173 
A NEW SPECIES OF PERONOSPORA. 
W. A. KELLERMAN. 
In the Spring of 1902 a Powdery Mildew was found, near 
Columbus, Ohio, on the False Mermaidweed, Floerkea proserpi- 
nacoides Willd. A quantity of the host plant remained in the 
collecting box over night, and when inspected the following day 
every specimen was found to be covered by the conidiophores 
uniformly distributed over the entire host. A few days later the 
same locality was visited but the unfavorable weather in the 
meantime proved disastrous to the fungus and unfortunately no 
additional material was obtained for thorough study of the par¬ 
asite. A search the following Spring was likewise unsuccessful, 
but ample material was obtained in May of the present year and 
the investigation so far as carried on to date is here reported. 
The host plants are dwarfed by the parasite though not dis¬ 
torted, and usually the entire plant harbors the fungus — all 
parts of the stem and leaves being evenly, though in the main 
rather sparsely covered by the conspicuous conidiophores. The 
shrivelled leaves and stems later however present a rather com¬ 
pact dull white layer of the richly branched and now collapsed 
conidiophores. Later infection is seen often restricted to the 
lower leaves of vigorous hosts but such cases are the exception 
rather than the rule. 
The conidiophores in their mode of branching, size, etc., as 
well as the conidia and zygospores, are almost the exact counter¬ 
part of the well known and widely distributed Peronospora para¬ 
sitica (Pers.) Tub, occurring on the various genera of the fam¬ 
ily Cruciferae. There is the very large and long main stem with 
the abundant and irregular branching near the apex. In the 
fungus on Floerkea however the main axis is relatively a little 
larger and the ultimate branchlets are also a trifle more elongated. 
The graceful curves of the latter are more pronounced in case of 
the Floerkean parasite and no small spurs or short tips leaving 
the branches at right angles, or presenting a runcinate appear¬ 
ance, were observed, — whereas in the Peronospora parasitica 
these are very often noticed. 
It should be stated that Peronospora parasitica causes, in 
some cases at least, slight distortion of the host. Sometimes 
there is evident hypertrophy in local areas, and there is often an 
unusual mode of branching and anomalous aspect of the plant 
which is attacked — all of which suggests that there is some 
radical difference between this fungus and the one occurring on 
Floerkea. Moreover, the Mildew on the Cruciferae is often re¬ 
stricted to portions of the stem or limited areas of the leaves — 
never the case, so far as observed, relative to the Peronospora 
now under consideration. 
