308 
Journal of Agricultural Research 
Vol. XXX, No. 4 
each juncture of axial filament and 
branch two of the elements deliver 
their contents into the third. Where 
evacuation is not too rapid, the 
delivery alternates in a more or less 
orderly manner, one or several zoo¬ 
spores from one arm being followed by 
one or several zoospores from the other. 
When discharge is more rapid, some 
degree of disorder usually results, a 
number of zoospores from both sources 
often being squeezed into the efferent 
element so compactly that they may 
momentarily appear as a single proto¬ 
plasmic mass (pi. 6, Cf) which further 
along in the course of the filament 
tends to become separated into its 
components. 
As in other members of the genus 
Aphanomyces, the changes (pi. 6, Ea, 
C), resulting in the division of the 
mycelial contents into zoospores, leaves 
the individual protoplasmic masses 
connected by a delicate strand of 
tenuous material. (PI. 6, Ed, D.) This 
strand can usually be seen without 
difficulty after evacuation has started, 
even when it has become further 
attenuated by lengthening of the inter¬ 
vals between successive zoospores. 
However, beyond the first juncture of 
two sporogenous elements the strands 
uniting the zoospores contributed by 
each of the elements are pressed against 
the confining mycelial wall by the 
interpolated zoospores contributed by 
the other, with the result that their 
continuity, if not actually destroyed, 
becomes at least very difficult to 
establish. After several junctures have 
been passed, so that the moving file of 
zoospores represents, perhaps, more 
than half a dozen interpolated series, 
it is certainly not possbile to make out a 
corresponding number of strands in the 
intervals. Usually only one or two 
can be made out in any particular gap, 
depending upon whether a strand can 
be demonstrated for one or for both 
of the two successive zoospores. (PI. 6, 
D.) Rothert (15) in his study of an 
unnamed species of Aphanomyces be¬ 
lieved that the strand persisted even 
where none was visible; that the fact 
of the escaping protoplasts being 
pointed at the ends indicated clearly 
enough the presence of a connecting 
medium capable of exerting a pull. To 
the traction exerted by the distal 
zoospores he assigned some importance 
in accomplishing the evacuation of 
the proximal ones. In the pea parasite, 
however, the zoospore while passing 
through the evacuation hypha are not 
always pointed at the ends, the an¬ 
terior end especially being frequently 
well rounded as if no distorting pull 
were present. 
A curious feature exhibited by the 
root-rot fungus which does not seem 
to have been recorded hitherto for any 
congeneric form is the discharge of the 
zoospores from a sporangial unit 
through plural evacuation hyphae. In 
the extensive units characteristic of 
vigorous young thalli converted to re¬ 
productive purposes, three or even four 
evacuation tubes have been found; and 
sometimes two of these may be close 
enough together that they can be ob¬ 
served simultaneously. Such an in¬ 
stance is represented in Plate 6, C. 
Evacuation here began through branch 
Cd and had proceeded briskly for about 
15 seconds when the tip of branch Cf 
also yielded. For a number of seconds 
discharge occurred simultaneously with 
about equal rapidity from both tubes, 
the element Ca supplying tube Cd, 
while Cf was supplied from the ele¬ 
ment Cc. Soon discharge through Cd 
came to a standstill, and the element 
Ca contributed its zoospores through 
the intermediate portion Cb into Cf, 
the latter then being fed, as Cd had 
been previously, from both directions. 
A number of zoospores in the portion 
Cb, that had originally come from Cc 
and seemed bound at the time to emerge 
through hypha Cd, thus reversed their 
direction and were discharged through 
branch Cf. In other cases evacuation 
through two tubes was observed to 
take place simultaneously through 
both, now through one, now through 
the other, in repeated and apparently 
haphazard alternations. The entire 
process, with its reversals in direction 
resulting in the discharge of successive 
zoospores through separate evacuation 
branches, failed to suggest any con¬ 
siderable effectiveness of visible and 
possibly invisible connecting strands 
in determining the course of any in¬ 
dividual zoospore. 
On emerging from the mouth of the 
sporangium the spores are cylindrical 
in shape, straight or slightly curved. 
(PI. 6, Ga.) Immediately, however, 
they begin to shorten up, and after 
passing through increasingly thick al¬ 
lantoid phases (pi. 6, Gb to e ), appear 
at the end of about 10 seconds as per¬ 
fectly spherical masses (pi. 6, Gf, 
although a certain proportion of ir¬ 
regular oversized individuals may usu¬ 
ally be found. (PI. 6 Be, Ce, Cg.) 
The secretion of a thin peripheral wall 
follows very shortly. While in certain 
species of Aphanomyces the quiescent 
zoospores arrange themselves in a very 
regular hollow sphere having some con¬ 
siderable degree of coherence, in the 
form under consideration these bodies 
show little tendency toward definite 
orientation and relatively little co- 
