Oct. 15, 1924 
Geranium Stemrot 
407 
of 100 sporangia from corn-meal agar 
plates average 21.85 m, with ranges 
from 16.4 fi to 27.26 Carrot agar 
and corn-meal agar are most favorable 
for their formation. They appear 
within four days after inoculation, on 
the upper surface of the agar, rarely 
within the agar or at the interface of 
agar and glass. 
The walls are smooth, thin, and hya¬ 
line. No papilla has been observed. 
The contents are hyaline and finely, 
uniformly granular, with a varying 
number of small, round, darker spots 
which are evidently nuclei, judging 
from comparison with stained sections. 
Newly formed sporangia are nonvacuo- 
late; older sporangia contain an irreg¬ 
ular central vacuole, which increases 
with age, and occupies one-fifth to one- 
half the diameter of the sporangium. 
The formation of the sporangia is 
readily observed in inverted blocks of 
corn-meal agar or in drops of oatmeal 
decoction, and presents the, usual 
features found in Pythium—the swell¬ 
ing up of a hyphal tip (or segment 
when intercalary) into a globular body, 
which is then cut off by a septum, with 
occasional continued growth of the 
hypha laterally in the case of sessile 
sporangia. They are not readily de¬ 
tached, and off ten germinate in situ. 
For about 10 days after their forma¬ 
tion the asexual fruiting bodies germi¬ 
nate by the extrusion of the undifferen¬ 
tiated contents through a short straight 
tube into an evanescent, delicately 
walled vesicle, where the zoospores 
are differentiated and whence they 
escape into the surrounding water. 
As older sporangia are placed in condi¬ 
tions favoring germination, the per¬ 
centage germinating in this manner 
decreases, and a greater number pro¬ 
trude a tube, which continues to grow, 
branches, and forms a mycelium. 
Both of these methods of germination 
have been watched repeatedly and are 
described below in detail (Pis. 4 and 5). 
A surface scraping near the point of 
inoculation of a 6-day-old corn-meal 
agar plate culture usually yields an 
abundance of sporangia, which may be 
placed for observation in a hanging 
drop of distilled water, previously 
aerated by a vigorous shaking of the 
bottle. Within 15 minutes a broad, 
thin-walled tube is seen protruding 
from most of the sporangia in the drop. 
The tube may issue from any part of 
the surface. Its contents are at first clear 
and highly refractive; later on granules 
from the sporangium gradually wander 
in. During the next 10 to 15 minutes 
the tube continues a slow growth, 
which ceases when a length of a third 
to half the diameter of the sporangium 
has been reached. In the meantime 
the sporangial contents have been in 
slow motion, the vacuole and., small 
dark spots changing their position 
gradually and irregularly. The tip of 
the tube suddenly blows out into an 
expanding bubblelike vesicle, whose 
wall is barely distinguishable from the 
surrounding medium; the sporangial 
contents ooze into it as it expands. 
The protoplasm within the sporangium 
breaks away from the wall opposite the 
tube, leaving lengthening fine strands 
attached to it. The vacuole, when 
present, does not appear to enlarge 
but is included in the general mass 
squeezing through the tube, and may 
break if too large. 
After the greater part of the con¬ 
tents has entered the bladder, the 
passage of the remainder gives the im¬ 
pression of a pulling through by the 
force of surface tension tending to 
round up the entire protoplasmic mass 
into the vesicle. Infrequently, part of 
the contents breaks off and remains 
within the sporangial. wall. Here it 
differentiates into a very few zoospores 
which fail to escape (PI. 4, H) and 
finally degenerate. 
The sporangial wall collapses slightly 
in places and becomes irregularly angu¬ 
lar. The contents are now clear ex¬ 
cept for a few irregular strands which 
connected the wall and the viscous de¬ 
parting protoplasm. The latter does 
not completely fill the vesicle arid is at 
first irregular in outline. It gradually 
assumes a smooth rounded form through 
the continued action of surface tension, 
and presents the same general appear¬ 
ance as when within the sporangium, 
except that considerably more space is 
occupied owing to imbibition of water 
in the absence of rigid confining walls. 
After a short period of quiescence, clear 
furrows and wedges appear on the pe¬ 
riphery, from which vague lines of de¬ 
marcation grow in toward the center of 
the mass. A rocking movement begins 
and increases in vigor as the lines be¬ 
come clearer and delimit definite re- 
EXPLANATORY LEGEND FOR PLATE 3 
A—Oospore and mycelium, in turgid cells. Stained. Oospore contracted, antheridium lobed 
B. —Oospores in crushed cells. Stained. Antheridium appressed; oosphere immediately subjacent 
C. —Section of pith. Note turgid infected cells, demarcation, crushed cells, and cavity 
D. —Oospores in crushed and turgid (at:r) pith cells 
