306 
Journal of Agricultural Research 
Vol. XXX, No. 4 
subjected to the treatment outlined 
above. Under favorable conditions 
almost the entire thallus appears 
to become involved in sporogenesis, 
the individual sporangia often consist¬ 
ing of axial filaments from 1 to 2 mm. 
long and bearing from 6 to 10 well- 
developed branches. (PI. 6, A.) The 
numbers of spores discharged from 
such extensive sporangial units is 
naturally very considerable, not in¬ 
frequently running up to 300 or 400. 
(PI. 6, Be.) The individual sporangia 
are set off from adjacent sporangia, or 
still undifferentiated hyphae by parti¬ 
tions which may be plane or somewhat 
curved and are often inserted at the 
origin of a branch. (PI. 6, A, D.) A 
vast number of zoospores may thus be 
produced in the course of a few hours, 
estimates made on such material 
often reaching several hundred thou¬ 
sand. It may be mentioned that the 
amount of growth observable after 
the washing away of the nutrient 
material is quite negligible, the pos¬ 
sibility of extensive proliferation of 
new filaments originating as specialized 
organs being thus largely precluded. 
Nor do the sporangial units of such 
material differ in abundance of branch¬ 
ing from the mycelium of the vege¬ 
tative thallus in an actively growing 
condition, in spite of the customary 
characterization of the sporangia of 
congeneric forms as simple or rarely 
branching. 
A distinction between hypha and 
sporangium might more plausibly be 
drawn when older material is used ; for 
the production of zoospores. Staling 
effects are here manifested in the de¬ 
generation of the contents of a large 
proportion of the hyphae. Sporogenesis 
is never prompt, a period of 48 hours 
usually elapsing before any consider¬ 
able discharge occurs. The reason for 
such delay is evident on examination, 
when it will be found that the old 
hyphae are not functioning as sporangia; 
that these have, in fact, become evacu¬ 
ated, the contents having apparently 
been utilized in the production of new 
filaments in the central portions as well 
as at the margins of the thallus; and 
that sporogenesis is localized in the 
newly proliferated filaments, which 
indeed, show relatively little branch¬ 
ing. Manifestly the potentiality of 
serving as sporangium is not limited to 
hyphae arising as specialized organs; 
but is inherent in any vigorous hyphae 
when given the necessary conditions. 
It may be remarked that Rothert (15) 
in his study of a congeneric form came 
to an entirely similar opinion in regard 
to this phase of reproduction. 
While the hyphae of the pea para¬ 
site in liquid culture, as within the host 
cell, tend toward evenness in diameter, 
pronounced local irregularities in re¬ 
spect to this dimension not being 
characteristic of the fungus, the ter¬ 
minal mycelial branches generally ex¬ 
hibit gradual attenuation toward the 
tip, the apical portion generally meas¬ 
uring 4 ju, or, more rarely, somewhat 
less. Evacuation of the individual 
sporangia very regularly takes place 
through these attenuated branches. 
As the protoplasmic masses pass from 
the larger hyphae into the constricted 
region they become considerably elon¬ 
gated and move at a proportionately 
increased speed. Thus a cylindrical 
mass 10 to 12 p in length, occupying 
the lumen of a filament 9 p wide and 
moving at a speed of about 35 p a 
second, on reaching the distal portion 
of the evacuation hyphae will be found 
measuring 30 to 50 p in length and 
moving more than 100 p a second. In 
a few instances a considerable part of 
the discharge tube was found reduced 
to a diameter scarcely exceeding 3 p. 
Discharge here offered the remarkable 
spectacle of zoospores drawn out into 
threadlike bodies, about 2.5 p in 
diameter and 70 to 90 n long, speeding 
along at the rate of approximately 300 
P per second. 
The discharge of the zoospores from 
the freely branching sporangium pre¬ 
sents an interesting complication. At 
EXPLANATORY LEGEND FOR PLATE 6 
Stages in asexual reproduction of Aphanomyces euteiches. X470 
A. —Portion of extensive sporangium drawn in three contiguous sections bearing six successive branches. 
ab-g, evacuation of zoospores arrested after proceeding for some time 
B. —a, Portion of sporangial unit with aggregation of approximately 350 zoospores 
C. —a to c, Portion of sporangial unit, evacuated at beginning only through branch cd, then through 
both cd and c/, and finally only through cf 
D. —Portion of sporangium 15 seconds previous to discharge through branch dc 
E. —a to d, Successive stages in the conversion of hypbal contents into zoospores ready for discharge 
F. —Zoospores rounded up within sporangial wall 
G —a to/, Successive stages in rounding up of cylindrical protoplasts, at intervals of 2 seconds 
H. —a to f t Evacuation of encysted zoospore , 
I. —a to e, Motile zoospores treated with osmic acid and gentian violet, showing length and insertion of 
flagella 
J. — a to/, Direct germination of encysted zoospores 
K. —a to d, Germination of zoospores after swarming and second rounding up 
