Feb. 15,1925 Root Rot of Peas Caused by Aphanomyces Euteiches 309 
herence. They seem merely to ac¬ 
cumulate promiscuously at the mouth 
of the sporangium' in an irregular lump 
(pi. 6, Be , Ce , and Cg), or where 
smaller numbers are concerned each 
individual may remain alone. 
The development of motile zoospores 
from these encysted bodies takes place 
after a period varying in some observed 
instances from to hours. A 
papilla makes its appearance on the 
cyst, measuring between one-fourth to 
one-third the diameter of the latter. 
(PL 6, Hb.) At first scarcely discerni¬ 
ble, it develops visibly in the course 
of several minutes, until it appears 
as a hemispherical protuberance. Sud¬ 
denly the granular protoplasmic con¬ 
tents begin streaming into the papilla, 
the tip of which thus becomes inflated 
into a spherical vesicle. (PI. 6 , He.) 
Streaming is completed within approxi¬ 
mately 10 seconds, the entire contents 
having then passed from the cyst into 
the vesicle. (PL 6, He.) The contour 
of the latter is not tangent to that of 
the empty cyst envelope, as these two 
structures are separated by a cylin¬ 
drical isthmus, about 1 y long, com¬ 
posed of the wall of the papilla. The 
whole process appears altogether anal¬ 
ogous to the discharge of the spor¬ 
angium of Pythium on a smaller scale, 
and, as in that genus, the discharged 
protoplast, after increasing distortional 
movements, finally develops motility 
and swims away, not as a number of 
zoospores, to be sure, but as a single 
zoospore, somewhat pointed at one 
end, with two cilia inserted laterally. 
(Pl. 6, Hf.) In material killed with 
osmic acid and stained with gentian 
violet, the flagella appear as thread¬ 
like structures approximately twice 
the length of the zoospore, one being 
somewhat longer than the other but 
the difference not being pronounced. 
(Pl. 6, la to e.) 
After swimming about for a variable 
period the zoospore, as in other mem¬ 
bers of the Saproligniaceae, finally come 
to rest and round up. Under favorable 
conditions they germinate, producing 
from one to three germ tubes (pl. 6, 
Ka to d) capable of extensive develop¬ 
ment into a mycelium, either in arti¬ 
ficial culture or in the tissues of a new 
host plant. 
It may be superfluous to call atten¬ 
tion to rather usual irregularities in 
development, cited frequently in the 
literature pertaining to related organ¬ 
isms. Among these might be men¬ 
tioned the failure of the zoospores to 
escape from the sporangium (pl. 6, F) 
and their germination within the fila¬ 
ment; the production of compound 
zoospores exhibiting two sets of flagella 
with erratic ineffectual movement, re¬ 
sulting from the germination of over¬ 
sized and evidently dienergid cysts; 
and direct germination, without swarm¬ 
ing, of encysted forms by the produc¬ 
tion of a single rather broad germ tube. 
(Pl. 6 , Ja to/.) 
TAXONOMY OF PARASITE 
As suggested in another connection, 
it is not improbable that the parasite 
under consideration may have been 
observed by previous workers investi¬ 
gating the troubles affecting peas. 
Wittmack (19), in Germany, attached 
the binomial Pythium sadebeekianum 
to a fungus found occurring as oospores 
in the roots of peas, the presence of 
which was evidently associated with 
symptoms having some similarity to 
those described in this paper. Chiefly 
because the diameter of oogonia, as 
given by this author, — 32 y is in excess 
over those of any species of Pythium 
commonly attacking higher plants, 
students of the latter genus have been 
at a loss as to the identity of the Ger¬ 
man fungus. Judging from the wide¬ 
spread occurrence of the root rot para¬ 
site in diseased pea roots in the United 
States, it is at least likely that Witt¬ 
mack, who apparently never observed 
sporangia in his material, may have 
assigned his fungus to the wrong genus. 
For quite similar reasons the same un¬ 
certainty attaches to Clinton’s (2, p. 
450-453) provisional identification of 
oospores observed during recent years 
in diseased pea roots in Connecticut as 
the oospores of Phytophthora cactorum. 
The identity of the forms observed by 
these writers with the fungus discussed 
in this paper at present can merely be 
suggested as a very fair possibility. 
In this connection it may not be 
amiss to call attention to the some¬ 
what unusual parasitic character of 
the rootrot organism when viewed in 
its taxonomic relation. While the 
Saprolegniaceae include a number of 
parasites affecting fish, only a few 
reports can be found of any members 
of the family attacking species of 
higher plants. In 1912 Sawada 5 pub¬ 
lished a paper containing a detailed 
study of Achlya prolifer a (Nees) 
DeBary, as the cause of a rice seedling 
* Sawada, K. investigation of the paddy seedling decay in Formosa. Formosa Agr. Exp. Sta. 
Spec. Bui. 3, 84 p., illus. 1912. [In Japanese.] Brief statement of content in English, by W. H. Weston in 
Ann. Bot. 37: 347-348,1923. Author’s unpublished English r6sum6 revised by W. H. Weston, deposited 
in Office of Cereal Investigations, Bureau of Plant Industry, Washington, D. C. 
