310 
Journal of Agricultural Research 
Vol. XXX, No. 4 
decay in Formosa. Nemec {12) in 
1913 described from Prague as the type 
of a new genus an interesting fungus 
causing swellings on the roots of Salix 
purpurea under the binmoia Jaraia 
salicis. It is worthy of note that the 
fungi in these two instances effected 
their parasitism under conditions sub¬ 
stantially aquatic, the willow plants 
attacked by Jaraia salicis being culti¬ 
vated at the time in tap water in the 
greenhouse, while the destruction ob¬ 
served by Sawada presumably occurred 
while the host was kept flooded. 
Within the genus Aphanomyces 
itself the tendency toward parasitism 
is moderately pronounced. Two of 
the eight described species, A. phyco- 
philus DeBary and A. norvegicus Wille, 
attack species of Spirogyra and Zyg- 
nema ( 1; 18); two other members of 
the genus according to Coker, A. 
stellatus DeBary and A. parasiticus 
Coker ( 3 ), attack Achlya, and the 
same author discusses a variety of A. 
laevis DeBary that was found growing 
parasitically on diatoms and desmids. 
In these instances the hosts represent 
aquatic lower forms attacked under 
thoroughly aquatic conditions. The 
only account of a member of the genus, 
and, indeed, of the family, as far as the 
writers have been able to determine, 
attacking one of the higher plants 
under ordinary terrestrial conditions is 
contained in the report by Peters {14) 
of a form of. Aphanomyces identified 
by him as A. laevis , as one of the three 
widely prevalent parasites responsible 
for root blight (Wurzelbrand) of sugar 
beets in Germany. Peters’ publication 
is of particular interest, although in 
some pathological features the disease 
he investigated differs from the trouble 
affecting the subterranean parts of 
peas. 
In considering the taxonomic dispo¬ 
sition of the pea fungus, moreover, 
Aphanomyces laevis represents one of 
the two species deserving of special at¬ 
tention, the other being A. helicoides v. 
Minden. The remaining six congen¬ 
eric forms are characterized by the pres¬ 
ence on the oogonium of spines or of 
tuberculate irregularities, whereas the 
oogonia of the pea parasite, like those 
of the two species designated, are en¬ 
tirely smooth on the exterior. Ac¬ 
cording to its author {11), A. helicoides 
is very similar to A. laevis, being dis¬ 
tinguished chiefly by a strong tendency 
in the antheridial branches to wind 
about the oogonium, or about ordinary 
hyphae, or even about other antheridial 
branches, in close helicoid turns. Cer¬ 
tain of Kasanowsky’s drawings {10: 
Taf. X, fig. 1) represent some such con¬ 
dition, making it seem probable that 
this investigator was dealing with a 
type more nearly resembling the Swiss 
form than the one originally described 
by DeBary. Coker seems inclined to 
support Von Minden’s own doubts con¬ 
cerning the validity of the helicoid 
habit as a specific distinction on the 
ground that a strong tendency toward 
such habit was exhibited by the typical 
form of A . laevis. Whatever disposi¬ 
tion may finally be taken with refer¬ 
ence to A. helicoides is, however, of 
minor concern here, for, as has been 
previously pointed out, no distinct tend¬ 
ency toward spiral growth has ever 
been found expressed in any of the cul¬ 
tures of the pea organism the writers 
have studied, although the branches 
bearing the sexual organs may be more 
or less involved after a more promis¬ 
cuous fashion. 
When the organism responsible for 
root rot of peas is compared with the 
typical aquatic form of Aphanomyces 
laevis, as revealed in the literature, a 
considerable measure of agreement be¬ 
comes evident. The dimensions and in¬ 
terrelations of oogonium and anther- 
idium and of the branches supporting 
them, as well as the dimensions of the 
oospores, correspond quite well in the 
two plants. A fair, even if not alto¬ 
gether perfect, agreement is evident in 
regard to size of zoospore and diameter 
of mycelium. The potentiality of the 
entire thallus to serve reproductive pur¬ 
poses by division into extensive branch¬ 
ing portions functioning as individual 
sporangia; the discharge of the latter 
through one or several hyphae tapering 
regularly toward the tip to a diameter 
inferior to the diameter of the mycelium 
generally; the ready germination of 
the oospores, and that without resting 
period or application of special treat¬ 
ment—these features point to a distinc¬ 
tion between the root parasite and the 
aquatic form, although it remains 
doubtful to what extent absence of their 
mention in the literature pertaining to 
the latter form is attributable to actual 
difference in its behavior or to short¬ 
comings in our knowledge concerning it. 
With regard to another character— 
namely, the thickness of the oogonial 
wall—it becomes almost impossible to 
entertain similar doubts. The ac¬ 
counts of Aphanomyces laevis given by 
DeBary, Humphrey {5), Kasanowsky, 
and Coker contain no reference to this 
feature, yet it is altogether unlikely that 
any of these investigators could have 
seen a structure of such extraordinary 
thickness without in some way re¬ 
ferring to it. Indeed, on the contrary, 
Coker in his definition of the genus 
