Feb. is, 1925 Root Rot of Peas Caused ly ApJianomyces EuteicJies 
303 
thick oospore wall disappears as such, 
being reduced to a delicate membrane, 
which yields to the enlargement of the 
protoplast and is pressed against the 
inner surface of the oogonial wall, with 
the result that the appearance is pre¬ 
sented of the oogonial cavity being en¬ 
tirely filled with protoplasmic contents. 
These contents, moreover, no longer 
exhibit the geometrical arrangement of 
the resting condition, but show instead 
a more or less uniformly granular 
condition. 
If the conditions are such as to favor 
direct germination, one or several pro- 
turberances are now thrust through the 
oogonial wall. (PI. 5, G, H.) The 
communications established by the fer¬ 
tilization tubes seem to serve an impor¬ 
tant r61e as channels of egress, as the 
granular germ processes can frequently 
be clearly seen passing through them 
into the antheridial cavity and thence 
emerging by a perforation through the 
antheridial wall; and owing to the col¬ 
lapse of the empty antheridia and diffi¬ 
culties in observation, instances of such 
utilization of these aperatures are very 
probably even more numerous than 
could be definitely established. In 
many cases the germ tube immediately 
gives rise to a number of branches, usu¬ 
ally aggregating about a dozen, which 
thus occur in rather crowded, bristling 
arrangement not at all typical of myce¬ 
lial ramification in the species (PI. 5, 
L, K); in other cases branching is de¬ 
layed until the germ tube has attained 
considerable length, and the sort of ram¬ 
ification then exhibited is altogether 
comparable to that shown by the thallus 
of the fungus generally. (PI. 5, I, J.) 
Manifestly the conditions here repre¬ 
sented correspond to those found in the 
two organisms investigated by DeBary 
and Kasanowsky, respectively. In ap¬ 
pearance the resultant structures bear 
some similarity to those produced by the 
two types of direct germination of, for 
example, the sporangia of certain species 
of Phytophthora. They may, indeed, 
plausibly be explained in the same 
way—vegetative development of the 
oospore as a single energid, on the one 
hand, as contrasted with the develop¬ 
ment of multiple energids resulting 
from division processes incident to 
abortive zoospore production, on the 
other. 
When an oospore germinates by the 
production of zoospores, a single fila¬ 
ment is produced which ceases elonga¬ 
tion after attaining a length varying 
from 8 to 12 times the diameter of the 
oogonium. (PI. 5, E.) The germ 
hypha regularly decreases in width 
toward the tip, the distal portion usu¬ 
ally measuring about 4 ju in this dimen¬ 
sion, or somewhat less than one-half 
the diameter of the basal portion. At 
this stage, when only approximately 
half of the oogonial contents have 
passed into the germ hypha, zoospore 
formation is initiated. In the germ 
hypha the process-shows no departure 
from the usual course that has been 
described so frequently in the fila¬ 
mentous vegetative sporangia of other 
members of the genus, yielding from 
6 to 10 cylindrical portions of proto¬ 
plasm connected, at least for a time, 
by a greatly attenuated strand. (PI. 
5, A.) It appears probable that de¬ 
velopment is in the main acropetal, the 
divisions delimiting the two or three 
most distal portions having been ob¬ 
served to be initiated after the separa¬ 
tion of the basal portions had been 
effected, the last division of all setting 
off the terminal portion. Within the 
oogonial wall the residual material 
which has become concentrated in a 
subspherical mass near the orifice of 
the germ hypha undergoes similar 
cleavage, as evidenced by its segrega¬ 
tion into lumps that become increas¬ 
ingly distinct and after some mildly 
writhing movements assume individ¬ 
uality as independent subspherical 
protoplasmic masses. (PL 5, A.) Sud¬ 
denly the tip of the germ hypha gives 
way and the protoplasmic masses es¬ 
cape one by one in rapid succession, 
each rounding up and encysting near 
the orifice. An interesting feature in 
the evacuation of the germ sporangium 
is that the globose bodies within the 
oogonium enter the germ hypha at the 
base to replace distal ones by stream¬ 
ing through the small aperture in the 
oogonial wall and assuming the cylin¬ 
drical form of the filament. In the 
course of about 10 seconds the entire 
apparatus is emptied. (PI. 5, B.) 
The discharged spores are scattered 
loosely about near the mouth of the 
germ hypha or collected in whole or in 
part in a loose irregular aggregation. 
(PI. 5, C, D, and F.) They number 
generally from 13 to 18 (most fre¬ 
quently 15), depending apparently 
somewhat on the size of the oospore 
and the proportion of oversized indi¬ 
viduals capable of producing one com¬ 
pound or two normal motile forms. 
While sporangial germination of the 
oospore does not appear to have been 
recorded hitherto for any species of 
Aphanomyces, it may be mentioned 
that a somewhat analogous develop¬ 
ment was noted by Sorokine (16) in the 
germination of globose bodies belong¬ 
ing to A . stellatus, which he designated 
as conidia. An extensive rupture in 
