Wilson: North American Peronosporales 
71 
P. Fagi 
P. Cactorum 
P. Syringae 
Mycelium: 
Hyphae slender, regular, 
intercellular, in cul- 
ture submerged, api- 
cally monopodially 
much branched. 
Haustoria simple or 
ganglionate and di- 
gately branched, cyl- 
indric. 
Conidiophores sympodi- 
ally branched and 
thickened below the 
conidia. 
Conidia elongate ovate, 
papillate, apex thick 
walled, produced tar- 
dily, size 40-74 X 30- 
32 p. 
Oospores : 
Oogonia globoid, in- 
tercallary, seen only 
in water cultures. 
Antheridia borne near 
the oogonium, tube 
not seen, relation to 
oogonium indefinite, 
Oospore with medium 
thick, smooth, yellow 
wall, size 30 71- 
Slender, regular, intercel- 
lular or intracellular, in 
culture both aerial and 
submerged, apically 
scantily monopodially 
branched. 
Simple or branched, cyl- 
indric, or apically en- 
larged irregularly. 
Sympodially much 
branched and thickened 
below the conidia. 
More or less regularly 
ovate, papillate, pro- 
duced abundantly, size 
30-40 X 15-30 ju. 
Pyriform, rounded at base, 
intercallary, seen in 
water and agar cultures. 
Borne near the oogonium, 
tube present, applied 
basally. 
With medium thick, smooth, 
yellow wall, size 20-3071. 
Very irregular in form, in 
culture both aerial and 
submerged, somewhat ir- 
regularly branched. 
None. 
Not typical sympodial in 
branching, conidia often 
borne in clusters. 
Roundish to ovate, very 
noticeably papillate, very 
variable in shape and 
size. 
Globoid, apical, seen in 
both water and agar 
cultures. 
Borne near the oogonium, 
rarely seen in water cul- 
tures, applied laterally. 
With medium thick, 
smooth, brown wall, size 
30-45 M- 
As a result of this comparative study it is very evident that 
these three forms are distinct species. The next question to 
present itself is that of the identity of the form which De Bary 
studied and named P. omnivora. From the evidence presented 
by De Bary in his paper Himmelbaur is inclined to the belief that 
the form was at least similar to P. Pagi, if not identical with it. 
In old agar cultures which had begun to degenerate forms ap- 
pear which are suggestive of Vaucheria, from which the author 
concludes that the genus Phytophihora may represent a degen- 
erate state of Vaucheria. 
The phenomenon of zonation in cultures was studied and the 
conclusion reached that it is due to variation in temperature. 
10. Phytophthora Syringae (Klebh.) Ivlebh. 
This fungus has been studied by three investigators who agree 
as to its morphology. Klebahn (1909) published a comprehen- 
