Oct, 15, 1924 
Geranium Stemrot 
419 
with rounded tips. Sporangia are 
abundant in culture media, and are 
regularly oval to spherical. Germina¬ 
tion is by extrusion of the undiffer¬ 
entiated contents through a short tube 
into an evanescent vesicle in which the 
zoospores are differentiated; germina¬ 
tion by tube takes place in older 
sporangia. Proliferation has not been 
observed. 
7. The oospores are smooth walled 
and lie free within the smooth oogonia. 
The latter are borne at the tips of 
slender branches. The antheridia are 
particularly characteristic, varying 
from a trumpet form to a broad, 
irregularly lobed mass clasping and 
fused with a large part of the oogonial 
surface. 
8. Fertilization takes place by direct 
passage of the antheridial contents 
through a hole in the fused oogonial 
and antheridial walls into the con¬ 
tracted and immediately subjacent 
oosphere. A fertilization tube has 
not been observed. 
9. Formation of the exospore wall 
is initiated by the peripheral spread of 
a narrow, clear band (a disk in 3 dimen¬ 
sions) within and around the smooth 
outlined oosphere, completely enclos¬ 
ing it. 
10. Viability and cultural characters 
on 16 media are given in detail. 
11. Optimum growth takes place at 
30° C. The maximum temperature 
is 35.5°; the minimum 5° (144 hours). 
12. Comparison of the Pythium type 
of zoospore formation with that in 
other genera points (a) to the greater 
intrinsic efficiency of the former type 
in view of the advantages herein dis¬ 
cussed resulting from emergence of 
undifferentiated contents en masse, 
and the fragility of the vesicle mem¬ 
brane; ( b ) to an interpretation of this 
type as an adaptation which secures 
minimum waste of spore-forming ma¬ 
terial combined with maximum ease 
of dissemination, at the expense, how¬ 
ever, of protection at a critical stage. 
That it did not become fixed in de¬ 
rived genera is an expression of the 
general evolutionary tendency toward 
protection of offspring rather than 
facility in dissemination. 
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