reb. is, 1925 Root Rot of Peas Caused by Aphanomyces Euteiches 
301 
large, spherical, somewhat eccentric, 
vacuole-like body of apparently homo¬ 
geneous structure, surrounded by a 
matrix containing numerous small 
uniform granules in regular concentric 
arrangement. The literature on the 
genus Aphanomyces like that on the 
Saprolegniaceae in general, shows some 
difference of opinion with reference to 
the nature of these internal elements, 
the large central body sometimes being 
referred to as an oil globule (I, 3 , p. 
160); while evidently at other times 
( 3 , p. 10) it is regarded as being of a 
protoplasmic nature and the granule- 
like structures as consisting of oily 
matter. Since the small peripheral 
granules stain well with Sudan III in 
the species under consideration, it 
would seem the latter view is probably 
more nearly correct, although the 
apparent homogeneity of the material 
constituting the central globule can 
not be regarded as characteristic 
generally of protoplasm. 
The relationships of the sexual ap¬ 
paratus can be studied to excellent 
advantage when the fungus is grown 
on hard corn-meal agar. By cutting 
off a thin surface layer of the sub¬ 
stratum, a thin preparation is obtained 
containing the thallus at nearly a uni¬ 
form optical level without any serious 
disruption of the structures concerned. 
Typically, and at least in the large 
majority of cases, the male and female 
organs arise from hyphae which show 
no close organic connection. The 
oogonium is apparently always term¬ 
inal, being generally borne on a rather 
short stalk arising as a lateral branch 
from a hypha usually of more than 
ordinary diameter. The antheridial 
branch generally arises from a less 
stout filament, which in many instances 
will be found to cross the larger filament 
close to the points from which the 
sexual branches have their origin. (PI. 
4, A to H.) Usually the antheridial 
stalk becomes intimately involved with 
the oogonial stalk after making a 
partial turn about the latter, although 
the condition described by Von Minden 
(11) for his Aphanomyces helicoides, 
and figured by Kasanowsky (10) in 
his account of A. laevis , in which the 
antheridial stalk makes several distinct 
turns about the oogonial stalk, has 
never been found realized. A number 
of short diverticulate branches often 
are borne on the hypha from which the 
antheridial branch originates (pi. 4, 
A, B, E, H) and occasionally on the 
hypha to which the oogonial stalk is 
attached. (PL 4, C, E.) As far as 
can be determined, they serve no 
special purpose, but add to the charac¬ 
teristic involved appearance of the 
apparatus, thereby further enhancing 
the optical difficulty in resolving it 
with certainty. 
The antheridial branch may be 
simple or branched, the branching 
frequently occurring near the base of 
the oogonium or a short distance from 
the base. Usually it is limited to a 
single bifurcation (pi. 4, B, H), but 
instances in which one (pi. 4, A) or 
both (pi. 4, F) of the resulting elements 
branched again have been found, one 
of the ultimate elements then some¬ 
times failing to develop any male 
organ. (PI. 4, D, F, G.) The anther- 
idium is always an expanded structure 
set off from the stalk by a septum, 
which is frequently curved with the 
convexity protruding into the interior. 
Often the antheridium appears sharply 
arched in the manner of a measuring 
worm, the fertilization tube in such 
instances usually being produced in the 
region where the distal lobe is in con¬ 
tact with the oogonium. (PI. 4, B, H.) 
Not rarely a hyphal diverticulum is 
present as a dorsal appendage (pi. 4, 
E, F) quite similar in appearance to 
analogous protuberances that can be 
observed occurring singly on the male 
organs of some species of Pythium 
and, as in the latter forms, apparently 
not serving any evident purpose. 
In some instances when the anther¬ 
idium attains unusually large propor¬ 
tions a transverse septum may be in¬ 
serted, generally at a constriction. (PI. 
4, A, G.) The resulting structure may 
evidently be regarded either as two 
male organs developed in series on the 
same stalk or as a compound anther¬ 
idium. Sometimes both of the male 
elements thus delimited have been ob¬ 
served communicating with the interior 
of the mature oogonium by independent 
tubes or apertures in the oogonial wall. 
While the origin of the antheridial 
branch near the base of the oogonial 
branch and a sort of contact relation 
of the two are of common occurrence 
and characteristic of the fungus, male 
stalks altogether unrelated to the 
oogonial stalk in place of origin also 
occur. As the number of antheridia 
to an individual oogonium varies from 
one to four, or even five, considerable 
variety in origin may be expressed in a 
single sexual apparatus. 
The oogonia and oospores developed 
in culture are quite similar to those 
found in diseased host tissue, but a few 
details not easily observed in the latter 
substratum may here be studied to ad¬ 
vantage. Thus the peculiar thick¬ 
ening of the oogonial wall will be seen 
produced into the distal portion of the 
supporting stalk, diminishing rather 
markedly, so that the latter is repre- 
13952—25f-2 
