412 
Journal of Agricultural Research 
Vol. XXIX, No. 8 
The protoplasm in both antheridium 
and oogonium is nonvacuolate and at 
first finely granular. The oogonial con¬ 
tents gradually become denser and 
lumpy and undergo a slow irregular 
motion, accompanied by the appear¬ 
ance and disappearance of darker 
particles similar in shape and size to 
the nuclei observed in stained sections. 
The antheridial contents have also be¬ 
come coarser but remain much more 
hyaline. Considerable pressure is ex¬ 
erted by the closely appressed antheri¬ 
dium, evidenced by the depression of 
the oogonial wall and the consequent 
irregularity of the otherwise spherical 
oogonium. 
Contraction of the oosphere is initi¬ 
ated by the appearance of irregular 
clear wedges at the periphery, first 
visible near the region of attachment 
to the antheridium and progressing 
around the periphery until the oosphere 
acquires a lumpy, irregularly oval 
shape, separated from the wall by a 
perfectly clear space except for occa¬ 
sional thin protoplasmic strands. The 
antheridial contents have also under¬ 
gone a slow, irregular streaming and 
appear most hyaline at the base near 
the septum. 
When the oosphere has fully con¬ 
tracted, it is invariably found in close 
contact with some part of the wall fused 
with the antheridium. A fertilization 
tube has not been observed, although 
dozens of fruiting bodies have been 
watched at this stage; nor have stained 
sections so far indicated more than a 
fusion of antheridium, oogonium, and 
a flow of antheridial content into the 
subjacent oosphere, through a break in 
the region of fusion. In living material a 
slow emptying of the antheridium may 
be seen at this stage. In the few cases 
where fertilization took place in the 
optical plane a cylindrical mass of 
protoplasm could be seen slowly pro¬ 
gressing from the antheridium into the 
oosphere through a clear space in the 
fused wall (PI. 5, C, b). An interface 
between the two masses of protoplasm 
was clearly visible, but was wavy and 
irregular, not smooth, like the fertiliza¬ 
tion tube of P. de baryanum , which 
was also kept under observation. 
The antheridium is left empty except 
for a few strands and a large oily globule 
at the mouth. 
After fertilization the irregularly 
contracted oosphere quickly rounds up 
into a smooth ball, slightly increased 
in volume. Oospore wall formation is 
initiated by the appearance of a short 
very narrow clear strip (PL 5, C, d at x) 
at some point tangentially within the 
periphery of the oosphere; this extends 
slowly around the circumference until 
the contents are inclosed by a narrow 
clear band, whose outer edge is per¬ 
fectly smooth and circular, the inner 
edge being uneven and warty. (PI. 5, 
C, d , e,f .) A contraction begins, similar 
to that of the original oosphere, except 
that a perfectly homogeneous refrac¬ 
tive material is left in the wake of con¬ 
traction. This proceeds until the full 
thickness of the wall is laid down, 
whereupon the irregular periphery of 
the contents smooths out into a circle. 
In the meantime the contents have 
become less lumpy and more finely 
granular; two dark round bodies may 
be seen in the center, probably the 
fusion nuclei; a vacuole appears and 
enlarges, and minute oily globules 
appear in the surrounding protoplasm. 
The antheridium shrinks and remains 
attached to the oogonial wall as the 
oospore attains maturity. Oospore 
germination has not been observed. 
CULTURAL STUDIES 
Growth of this fungus was studied 
on 16 media in four culture series, each 
of which included triplicate inocula¬ 
tions on all media. Cultures were 
kept in the dark at room temperature 
(18° to 25° C.) for three months. In 
the main the terminology suggested 
by Harsch and Long (11) has been fol¬ 
lowed. Comparisons over a four-year 
period with the other three Pythium 
spp. have shown a constancy of char¬ 
acters of definite diagnostic value, 
which has emphasized to the writer 
the necessity and the feasibility of a 
standardized procedure and terminol¬ 
ogy for the study of cultural charac¬ 
ters of fungi, such as is available to 
the bacteriologist. Growth on these 
media is described below: 
Corn-meal agar. —Upper half of 
slant covered with downy white aerial 
growth, becoming loose and cobwebby 
toward base of tube, flattening down 
after two weeks to form a hyaline, 
smooth, sodden mat; closely parallel 
hyphse at edge of colony, resulting in a 
striking combed-silk effect when viewed 
by transmitted light; irregular radiat¬ 
ing patches of varying density in older 
part of colony. Growth on corn- 
meal agar plates prostrate and sub¬ 
merged; otherwise similar to growth 
in tubes (PI. 1, B). Differ markedly 
from other Pythium spp. in the combed- 
silk effect. 
Corn-meal flasks. —Felted, com¬ 
pact white growth forming a dry mat 
about 2 or 3 mm. thick. Differs only 
in forming the more compact growth. 
Oatmeal agar. — White aerial 
growth well defined after five days, 
loose and cottony, but more compact 
in central part of colony; after 14 days 
