302 
Joui'nal of Agricultural Research 
Vol. XXX, No. 4 
sented in its proximal portion in an en¬ 
tirely unmodified form. An interest¬ 
ing variability is exhibited by the par¬ 
tition delimiting the oogonial cavity at 
the base. Usually it occurs as a rather 
inconspicuous cross wall inserted in the 
distal portion of the stalk, providing no 
marked interruption in the roughly 
subspherical interior surface of the 
oogonial envelope. (PI. 4, A, F, H.) 
It sometimes projects into the interior 
as a convex columella-like structure, 
and in some cases such development 
may be so pronounced that the avail¬ 
able space is greatly reduced, constrain¬ 
ing the oospore to adopt a distinctly 
ellipsoidal shara, with the major axis 
transverse to the axis of the oogonium. 
(PI. 4, G.) Such modification may 
perhaps best be regarded as a fortui¬ 
tous morphological peculiarity rather 
than as an abnormality, being present 
in material derived from the diseased 
host as well as in culture and evidently 
not adversely affecting the vitality of 
the oospore. 
The processes of fertilization are not 
as amenable to direct observation as 
might be desired, for although an 
abundance of antheridia and oogonia 
develop readily in liquid culture, and 
consequently can be obtained in Van 
Tieghem preparations, their contents 
appear to degenerate at an early stage, 
or an oospore will be produced of a 
patently abnormal character, exhibit¬ 
ing a promiscuous granular or irregu¬ 
larly vacuolate internal structure. Ex¬ 
amination of preparations of corn- 
meal-agar cultures abounding in nor¬ 
mal sexual conditions indicate that 
wjien several antheridia are present, as 
is usually the case, all or several of 
them may develop fertilization tubes. 
For example, out of three or four an¬ 
theridia attached to an individual fe¬ 
male cell, two or three may usually be 
found to communicate with the inte¬ 
rior of the oogonium by openings 
through the thick oogonial wall. While 
not all of the antheridia provided with 
such communications appear devoid of 
contents, it is certainly not unusual to 
find two male organs from which the 
protoplasm has disappeared completely 
or almost completely. (PI. 4, A, F, H.) 
It is readily apparent that such a con¬ 
dition might be brought about by de¬ 
generation quite as well as by evacua¬ 
tion of contents into the oogonium. In 
a cytological study of a congeneric 
species, Kasanowsky (10) found that 
after fertilization was effected by one 
antheridium the nucleus of a second 
antheridium was intercepted in its 
passage through the fertilization tube. 
No statement is made by this author 
whether or not any transfer of cytoplas¬ 
mic material may take place from a 
second antheridium previous to the en¬ 
trance of the nucleus into the tube and 
its interception. The empty condition 
of plural antheridia, frequently en¬ 
countered, points to such possibility. 
It is even not inconceivable that where 
nuclear degeneration is as easily ef¬ 
fected as in the sexual apparatus of the 
coenocytic type, to which Aphanomyces 
seems to belong, the entrance of a su¬ 
pernumerary nucleus may not bring 
about as impossible a cytological situa¬ 
tion as sometimes has been assumed. 
GERMINATION OF OOSPORES 
The germination of oospores of Aph¬ 
anomyces appears to have been re¬ 
corded for only two species, DeBary ( 1) 
having observed the process in mate¬ 
rial of Aphanomyces stellatus De Bary 
that had been kept in water for three 
months, and Kasanowsky (10) in ma¬ 
terial of a form he designated as A. 
laevis, DeBary, after this had passed 
through a resting period of over seven 
months. In both cases a germ tube 
was produced which perforated the 
oogonial wall and developed into a my¬ 
celium. A difference in the accounts of 
these authors may be noted in the 
promptness with which branching of the 
germ tube occurred, that of A. stellatus 
giving rise to a large number of hyphae 
very soon after emerging, if not imme¬ 
diately, while in Kasanowsky's fungus 
ramification was delayed until the tube 
had attained a length of 300 ju. 
Unlike oospores of the two species 
mentioned, those of the parasite attack¬ 
ing peas require no extended resting 
period. When material from 15-day- 
old corn-meal-agar cultures was trans¬ 
ferred to hanging drops in Van Tieghem 
cells, a considerable proportion of the 
oospores germinated, the method of 
germination, whether by mycelial de¬ 
velopment as observed by DeBary and 
by Kasanowsky, or by the production of 
zoospores which has not hitherto been 
recorded for any member of the genus 
Aphanomyces, seemingly being de¬ 
pendent to a great extent on the amount 
of nutrient material incorporated in the 
preparation. Thus Van Tieghem cul¬ 
tures prepared from material without 
any preliminary washing or removal of 
particles of substratum quite invariably 
exhibited direct germination into a my¬ 
celium. When the material was first 
allowed to soak, and the bits of solid 
food material removed as completely as 
possible, indirect germination by means 
of zoospores predominated. The ini¬ 
tial changes which take place during the 
first 24 hours appear to be the same, re¬ 
gardless of eventual developments. The 
