Feb. 15,1925 Root Rot of Peas Caused by Aphanomyces Euteiches 311 
Aphanomyces, recognizes a thin un¬ 
pitted oogonial wall as a generic char¬ 
acteristic, presumably common to all 
species; and all of the authors men¬ 
tioned figure the oogonial envelope of 
A. laevis as a thin membrane, not to be 
compared with even the least indu¬ 
rated of the homologous structures be¬ 
longing to the parasite on pea roots. 
In this connection it may be men¬ 
tioned that the writers have cultivated 
an aquatic species of Aphanomyces 
with smooth oogonia, obtained through 
the courtesy of J. A. Lounsbury, who 
isolated it from water of Lake Mendota, 
where apparently it occurs in some 
abundance. This fungus, which as far 
as could be determined answers to the 
description of A. laevis , very obviously 
is not identical with the parasite affect¬ 
ing peas, developing a heavy matted, 
submerged growth on various agar 
media entirely unlike the arachnoid 
growth characteristic of the terrestrial 
organism. The oogonia are produced 
much more sparingly and always with 
the thin membranous wall made fa¬ 
miliar by the figures of various writers. 
As the different isolations made from 
diseased peas compared with one 
another show unusual uniformity with 
reference to morphological character¬ 
istics, as well with reference to rapidity 
and character of growth on a variety of 
substrata, their incorporation in the 
same species with a form so evidently 
dissimilar as the aquatic plant could 
scarcely contribute to taxonomic clarity. 
The identity of Peters’ beet parasite 
remains problematical. This author 
undoubtedly was right in concluding 
that the measurements of his fungus, 
while somewhat different from those of 
Aphanomyces laevis , did not, in them¬ 
selves, justify its recognition as a 
species distinct from the latter. It is 
interesting to note that he observed 
very marked variability in thickness of 
both oogonial and oospore walls, and as 
the thickness of these structures fluc¬ 
tuated together he believed that the 
fluctuations were contingent on the 
same environmental conditions affect¬ 
ing both. Thus in material containing 
oogonia so thin-walled that they were 
found collapsed, the oospores borne in 
them were provided with walls only 3 m 
thick; while in other material oogonia 
with walls 1.5 m thick contained oospores 
of which the envelope measured 5 to 6 m 
in thickness. If the measurements of 
the oospore wall as given represent 
measurements of normal material, 
Peters’ fungus would undoubtedly con¬ 
stitute a species different from any 
species of Aphanomyces hitherto de¬ 
scribed, as well as from the one de¬ 
scribed in this paper. However, 
grounds for suspecting that this is not 
the case are not wanting. In the pea 
parasite, for example, degenerate con¬ 
ditions of the sexual apparatus are far 
from rare even on the most favorable 
substratum like hard corn-meal agar; 
when less favorable media are used 
(potato or carrot decoction with 1.5 
per cent agar, and also pea decoction 
in the absence of solid particles) de¬ 
generate conditions represent the over¬ 
whelming rule. The contents of the 
oogonium may become lumpy and de¬ 
generate before an oosphere is formed, 
or an oosphere may be formed but de¬ 
generate without forming a wall, or a 
wall may be formed but the contents 
degenerate instead of developing the 
normal structure. In any case swell¬ 
ing of the confining membrane is a 
regular concomitant of protoplasmic 
degeneration, whether this occur in 
oogonium or oospore, and in the ab¬ 
sence of normal material such patho¬ 
logical modification might be mistaken 
for normal thickening. In view of 
these circumstances, it is hardly pos¬ 
sible to decide definitely as to the 
morphological relationship of the two 
congeneric forms, both terrestrial in 
habitat and parasitic on a phanero¬ 
gamic host. 
It may also be stated that in the 
study of the pea organism structures 
involved in degenerative changes were 
not given weight; that the peculiarities 
of the oogonial wall submitted as 
normal were observed regularly in 
nature, as well as in culture, in individ¬ 
ual female organs containing oospores 
provided with a wall of moderately 
and practically unvarying thickness 
containing a large, homogeneous, 
slightly eccentric (“subcentric” in the 
phraseology used by Coker) structure, 
surrounded by concentrically arranged 
granular-appearing bodies. The para¬ 
site, it is believed, may best be re¬ 
garded as a new species. Because of 
the distinctive character of the oogonial 
envelope, the specific name euteiches is 
suggested. 
TECHNICAL DESCRIPTION 
APHANOMYCES EUTEICHES 
Drechsler n. sp. 
Parasitic on the subterranean parts 
of cultivated peas (Pisum sativum L.), 
causing a destructive stem and rootrot 
capable of affecting the growing host 
at all ages. 
Hyphae hyaline, branching at mod¬ 
erate intervals (20 to 150 m) at angles 
approaching a right angle; 4 to 10 m in 
diameter, the individual filaments not 
