June 1, 1925 
Comparative Studies of Pythium debaryanum 
1059 
again within three weeks, cottony at 
base, felted and compact at tip, matting 
down within three months. 
D. The aerial growth is loose and 
more closely appressed to the slant. 
CoRNMEAL AGAR TUBES. - A. Thin, 
prostrate hyaline mat, thicker toward 
base of slant, finely granular due to 
abundant conidia. No aerial growth, 
except a dried felty layer at the tip. 
B. Cobwebby white mycelium plug¬ 
ging tube up to half of slant, merging 
into a thin prostrate weft in the upper 
half; entire aerial mass flattens down 
to a gelatinous mat within two weeks. 
D. Aerial growth less abundant than 
B , completely matting in 10 days. 
Congo-red agar. — A. Scanty sur¬ 
face growth, except over lower half of 
slant, surface dry, shiny, abundant 
subsurface growth reaching throughout 
the agar, uniformly granular, conidia 
formed in abundance along the glass 
at the edge of the slant; prostrate 
except for cobwebby wefts at edges of 
slant appearing after two weeks. No 
color change after three months. 
B. Abundant white surface growth, 
becoming aerial within a week, loose, 
cobwebby; plugging tube three-fourths 
up-slant; quickly matting down (two 
weeks) to a thin dry layer of closely 
appressed hyphae, aerial mycelium 
around edges persisting; abundant 
uniform subsurface growth of more 
compact texture than A. No color 
change after three months. 
D. Differs from B in earlier and 
more abundant aerial growth, which is 
also much more compact and white 
and slower in matting down. No color 
change after three months. Note: 
Tubes of P. complectens showed a color 
change to Indian purple. 
VIABILITY 
Duplicate tube cultures of each 
organism on various media, which had 
been kept at room temperature (18° C. 
in winter to 35° C. in summer) were 
tested for viability as described for 
Pythium complectens. Melted corn- 
meal agar at 38° was poured over the 
slants after absorption of sterile oat¬ 
meal decoction; transfers from cultures 
which showed growth were compared 
with stock cultures and were also 
identified microscopically. The re¬ 
sults are summarized below. 
Isolation B. —Dead after 113^ 
months on potato agar, potato dex¬ 
trose agar, Soyka rice, beef agar, 
geranium agar, and in one tube of 
oatmeal agar; also after 7 and 8 
months on potato agar and Congo-red 
agar. Alive after 11^ months on corn- 
52243—25f-5 
meal agar, bean agar, and in one tube 
of oatmeal agar; also after 53^ months 
on potato dextrose agar. 
Isolation D. —Dead on all media 
kept longer than 53^ months. 
Isolation A .—Dead on all media 
kept longer than months, except 
on carrot agar where it was recovered 
after 9 months. 
The high viability of B as contrasted 
with that of the other two fungi, 
should be compared with the equally 
high viability of Pythium completions, 
which was recovered after 113^2 months 
on carrot agar and bean agar. There 
can be little doubt that the relative 
viability of these species of Pythium is 
correlated with the production of oo¬ 
spores, which is abundant in P. de¬ 
baryanum and P. completions and 
relatively scarce in the other two, 
as was pointed out in the description 
of their morphology. 
TEMPERATURE RELATIONS 
The accompanying chart (fig. 3) 
outlines the growth curves averaged 
from two experiments with plates in 
ice thermostats and warm incubators, 
ranging from 3° C. to 35.5°. Triplicate 
plates of cornmeal agar 'of each 
organism were placed in each compart¬ 
ment and measurements of the colony 
diameter were made at 24-hour inter¬ 
vals. Inoculations were made from a 
three-days old cornmeal agar plate 
culture which was cut up into one- 
sixteenth inch squares, each square 
then being planted in the center of the 
fresh plate. Before inoculation all 
plates were kept overnight in their 
respective compartments to avoid lag 
effects. 
The behavior of these fungi at the 
lower temperatures presents some in¬ 
teresting features. 
Isolation D shows the lowest mini¬ 
mum, the colonies growing appreciably 
at 6° C. within 24 hours, and reaching 
a diameter of 41 mm. in 144 hours 
(not shown on chart). Growth was 
evident at 3° within 48 hours, and, 
when placed directly on ice, showed a 
slow growth at 96 hours, a character¬ 
istic separating it immediately from the 
remaining Pythium species studied. 
In fact, the quickest way of differenti¬ 
ating this organism from the others 
was to place freshly inoculated plates 
in the lowest-temperature compart¬ 
ments; the plate showing the most 
growth, or in fact any growth at all at 
or near 6°, within 24 hours, could be 
counted on as being isolation D. 
Colonies of isolation B showed 
growth at 6° only after 72 hours, reach- 
