304 
Joumal of Agricultural Research 
Vol. XXX, No. 4 
the thick wall of these bodies through 
which the germ tube made its exit and 
their considerably inferior length pro¬ 
vide differences in detail. Direct ger¬ 
mination by a germ tube was also 
described for these conidia, the result¬ 
ing hyphae being of the more remotely 
ramifying type, generally characteristic 
of the growing mycelium. 
ASEXUAL REPRODUCTION 
It is presumably altogether safe to 
take for granted that the sexual spores 
developed in the tissues of the diseased 
host constitute the regular resting 
bodies of the fungus, by the germina¬ 
tion of which the parasite is reestab¬ 
lished in successive seasons. That by 
the production of germ sporangia they 
are also the chief means by which the 
fungus extends its distribution in the 
soil, appears at least very probable, 
although, as is well known, dissemina¬ 
tion of the aquatic members of the 
genus is effected by zoospores pro¬ 
duced in sporangia of mycelial origin. 
For when infected pea tissue contain¬ 
ing an abundance of the mycelium of 
the parasite is placed in water no 
extramatrical development takes place, 
the organism thus differing consider¬ 
ably in behavior from the amphibious 
species of Pythium or Phytophthora, 
for example, which are frequently 
found in similar relationship, as well 
as from the congeneric form reported by 
Peters {13, 14) as causing root rot of 
sugar beets in Germany. The pea 
parasite, however, continues in its 
development of sexual spores appar¬ 
ently uninterrupted. But even if zoo¬ 
spores could be produced by such means 
it is not certain, in view of the brief 
time elapsing between full mycelial 
development and the initiation of 
sexual stages, that extensive zoospore 
formation from mycelial elements 
could frequently be expected in nature. 
On the other hand, in artificial 
culture, the production of zoospores 
from the ordinary filamentous sporan¬ 
gia characteristic of the genus can be 
induced, and that in exceedingly great 
profusion. Following the well-known 
methods for cultivating aquatic forms, 
the parasite was grown in pea decoc¬ 
tion made by adding from 8 to 10 
freshly shelled peas to 100 cc. dis¬ 
tilled water in an Erlenmeyer flask 
and sterilizing by autoclaving or inter¬ 
mittent steaming. Altogether satis¬ 
factory results were also obtained 
by the use of canned peas with some 
of the liquor in which they were 
obtained, as well as by employing 
about twice the number of dried 
peas to the same quantity of water. 
Within three or four days at ordinary 
temperatures an extensive submerged 
mycelium was produced, appearing in 
the liquid medium as a translucent 
nebulous mat. The whole growth 
was now transferred to a deep Petri 
dish, the peas removed, and the 
mycelium washed several times at 
intervals of about 15 minutes with 
changes of sterile water. For con¬ 
venience in examination it was found 
desirable the last time to add only 
enough water to keep the mat sub¬ 
merged. 
With young thalli at a temperature 
of about 20° C., evacuation of the 
sporangial filaments was found to 
begin about six to seven hours after 
washing was completed. As in the 
case of the germ sporangia, the internal 
developments follow the course de¬ 
scribed for congeneric species by other 
writers. It may not be superfluous 
however, to discuss certain matters 
which perhaps have not received 
adequate treatment hitherto, or which 
involve points in regard to which the 
fungus under consideration would ap¬ 
pear to be at variance with its aquatic 
congeners. 
For example, in the writings of most 
authors the distinction is made between 
vegetative hyphae and sporangia. 
While these structures are invariably 
said to be similar to each other in ex¬ 
ternal morphology, the impression is 
conveyed that specialization in perhaps 
less obvious characteristics nevertheless 
obtains. Such a supposition, while con¬ 
serving the analogy to other Saproleg- 
niaceae, finds little support in the 
behavior of young vigorous thalli 
EXPLANATORY LEGEND FOR PLATE 5 
Oospores of Aphanomyces euteiches from 15 day old hard cornmeal agar cultures germinating in Van 
Tieghem preparations. X 470 
A.—Germ sporangium 30 seconds before discharge 
B .—Same sporangium 5 minutes later, after evacuation 
C, D.—Evacuated germ sporangia showing utilization by germ hypha of aperture in oogonial wall pro¬ 
duced by antheridium 
E. —Oospore with single germ tube previous to separation of contents 
F. --Evacuated germ sporangium 
G to J.—Direct germination of oospores by production of hypha with ordinary type of branching 
K, L.—Direct germination of oospore with close branching immediately after emergence of germ tubes 
