Oct. 15, 1924 
Geranium Stemrot 
417 
differentiated before emergence. Ros¬ 
enbaum, working with Phytophthora 
(16), states that “frequently for some 
reason a few of the swarmspores do not 
emerge with the majority.” In forms 
in which the vesicle occurs (accom¬ 
panied by preliminary differentiation 
in the original sporangium), he finds 
that “ after the liberation of the swarm¬ 
spores, the vesicles begin to contract, 
all signs of the opening disappear, and 
if any zoospores remain they are unable 
to escape.” Coker, in his recent mono¬ 
graph of the Saprolegniaceae (7), notes 
that “in both Saprolegnia and Achlya 
it frequently happens that the discharge 
of the spores is only partial, a few, or 
even a good many spores being left in 
the sporangium. These retained spores 
may emerge from their cysts as nor¬ 
mally, for a second swimming stage, 
moving about within the sporangium 
until they find their way out by its 
mouth, if they ever do.” 
Correlation of these observations 
indicates that the Pythium type of 
zoospore formation per se is by far the 
better mechanism for securing maxi¬ 
mum dissemination with minimum loss 
of spore-forming material for the fol¬ 
lowing reasons: 
(1) The migrating protoplasmic 
mass, covered as it is by a single 
plasma membrane, is kept together 
by cohesion and surface tension, both 
of which are powerful enough (except 
in rare and clearly pathological cases) 
to force the entire mass out as a whole, 
once emergence has been initiated by 
the propulsive force engendered by 
imbibition and swelling of a colloidal 
aggregate in the presence of an avail¬ 
able opening. The operation of these 
factors is clearly evident to anyone 
watching the pulling together of the mi¬ 
grating mass when half way through the 
tube, and its subsequent rounding up 
when wholly within the elastic vesicle. 
Compared with other genera, it is in 
sharp contrast with the emergence 
singly of a collection of fully formed 
zoospores, the vanguard of which must 
be subjected to the propulsive force 
of swelling, which is necessarily ex¬ 
hausted when the total potential 
swelling of the remaining individuals 
is equal to the volume of the sporan¬ 
gium; the exit of the remainder, as 
De Bary (4), Coker (7), and others 
have shown, is largely dependent on 
their connection with the preceding 
spores by delicate protoplasmic threads 
and ciliary entanglements rather than 
by their own unaided efforts. Con¬ 
sidering the fragility of these connec¬ 
tions and the miniature turmoil at the 
time of emergence, it is not surprising 
that zoospores are often left behind 
and fail to escape, as the above-quoted 
authors have observed. In the Py¬ 
thium type of egress, however, the 
entire sporangial contents are removed 
en masse and under one enclosing 
membrane, thereby incurring a mini¬ 
mum risk of wasting spore material 
by imprisonment in the sporangial 
walls. 
(2) Provision for maximum facility 
of dissemination, once the zoospores 
are formed, is secured in Pythium by 
the presence of an extremely tenuous, 
fragile membrane around the zoospore 
mass, capable of disruption with the 
greatest ease and thereby enabling all 
zoospores formed to swim away, as 
contrasted with the rigid walls sur¬ 
rounding the zoospores in other genera. 
These conditions and their results— 
emergence en masse and fragility of the 
vesicle membrane—point clearly to the 
above conclusion as to the greater 
intrinsic efficiency of the Pythium 
type of sporangial germination, and to 
the interpretation that this type con¬ 
stitutes a definite adaptation securing 
minimum waste of spore-forming ma¬ 
terial combined with maximum ease of 
dissemination. That it did not become 
the prevailing type in zoospore-forming 
fungi can be traced to another factor, 
the clue to which is afforded in the 
above-recorded observation that the 
delicate vesicle containing the undif¬ 
ferentiated mass was susceptible to 
impacts leading to mechanical injury 
and degeneration before zoospores 
could be formed. It is clear that 
maximum dissemination is here ob¬ 
tained at the expense of protection at 
a critical stage, such as is afforded in 
genera in which the zoospores are 
formed within the rigid sporangium. 
The great advantage of the latter 
method lies in the fact that' some at 
least of the swarmspores are sure to 
escape and perpetuate the race; in the 
Pythium type, the whole output of 
the sporangium is lost if the undif¬ 
ferentiated mass is mechanically in¬ 
jured in its exposed position. Evolu¬ 
tionary tendencies in matters of 
reproduction in higher plants and 
animals are in the direction of spe¬ 
cialized and well-protected off-spring 
in small numbers rather than along 
the lines of quantity dissemination of 
the unprotected many; it is only neces¬ 
sary to consider this to see that a 
specialized adaptation which secures 
the latter end, such as we have in 
Pythium—admirable a mechanism as 
it intrinsically is—yet insufficiently 
proof against unfavorable conditions, 
can not imprint itself permanently on 
derived genera. Hence, in the closely 
allied and probably derived Phy- 
