1038 
Journal of Agricultural Research 
Vol. XXX, No. 1 
would seem to require modification 
either by appropriately amending the 
two genera recognized by him or includ¬ 
ing one or more additional genera. 
For the present, therefore, it seems best 
to retain the genus Pythium in its more 
inclusive sense, as employed in the 
writings'of, DeBary and Butler. 
PATHOGENICITY 
The pathogenicity of the three strains 
isolated from material obtained on the 
markets of Washington, Pittsburgh, 
and Chicago was repeatedly demon¬ 
strated by inoculation into healthy 
cucumber fruits. Pieces of mycelium 
from pure cultures were inserted into 
aseptic incisions, which then were 
sealed with sterile vaseline, and the 
cucumbers placed in glass chambers 
without additional water. Softening, 
involving the tissues usually for a 
radius of several centimeters, was 
manifest within 24 hours; in 48 hours 
the larger part of the cucumber was 
involved and aerial mycelium was 
present in quantity near the point of 
inoculation,- while farther away it 
appeared in numerous small patches 
and minute white flecks that marked 
individual spots where the vigorous 
crowded hyphae had burst through 
the confining epidermis (pi. 1, A). 
At the end of the third day the whole 
fruit was frequently entirely clothed 
in cottony mycelium (pi. 1, B). That 
we are not dealing here with a special¬ 
ized parasite became evident when 
altogether similar results were ob¬ 
tained by the use of strains morpho¬ 
logically identical with those derived 
from the cucumber but isolated from 
other sources: (1) -From dead female 
nematodes, Heterodera radicicola (Greef.) 
Muller, in material supplied by N. A. 
Cobb and G. Steiner, where the occur¬ 
rence of the fungus as a saprophyte or a 
possible parasite invading moribund 
specimens could not be clearly deter¬ 
mined; (2) from pea ( Pisurn sativum, 
L.) roots exhibiting symptoms of root- 
rot; and (3) from watermelon fruits 
affected with the buff blossom-end 
rot. 
The cucumber parasite was tried 
opt on a number of other economic 
cucurbitaceous fruits. . As might be 
expected, watermelons were found 
highly susceptible to attack, the re¬ 
sulting decay being entirely similar 
to the buff blossom-end rot familiar 
to the writer as a field trouble appar¬ 
ently widely distributed in the Middle 
Atlantic States, and for the most part 
due to the identical fungus. Pattypan, 
vegetable marrow, and summer crook- 
neck squashes, all representing varie¬ 
ties of Cucurbita pepo L., are as prompt¬ 
ly attacked and destroyed as the cu¬ 
cumber and with the same luxuriant 
development of extramatrical mycelium 
(pi. 2, A, B). Experiments with musk- 
melons ( Cucumis melo L.) have not 
been quite as satisfactory, owing to the 
difficulty of avoiding bacterial con¬ 
tamination, especially in riper speci¬ 
mens. In general, it appears that in 
the green condition in which this fruit 
is frequently found on the market, the 
muskmelon does not provide a sub¬ 
stratum very suitable for the fungus, 
but that as maturity is approached 
the soft edible pulp is more readily 
invaded. It is possible that the fungus 
participates in the destruction of re¬ 
jected muskmelons left in the field; a 
considerable portion of the abandoned 
muskmelons in some Delaware fields 
visited by the writer in 1922 exhibited, 
as the initial stage in decomposition, a 
very watery condition of the interior, 
associated with the peculiar marshy 
odor fairly presumptive of the presence 
of some species of Pythium. 
When inoculated under the rind of 
honeydew melons and cassaba melons 
(Cucumis melo L.), the fungus is able 
to establish itself, but subsequent 
development is markedly slow, some¬ 
times being scarcely one-tenth as rapid 
as in cucumbers. The mycelium found 
in the tissues is of a compact, densely 
branching type, similar to that ob¬ 
tained on artificial media excessively 
rich in food materials, indicating that 
the juices of these fruits are too con¬ 
centrated to permit of normal growth. 
Several inoculations into the flesh of 
Hubbard squash ( Cucurbita maxima 
Duchesne) failed to result even in in¬ 
cipient infections, although the possi¬ 
bility that this vegetable is amenable 
to attack under other and more favor¬ 
able conditions is not be to excluded. 
While decay of cucumbers in transit 
has hitherto been found associated with 
only one species of Pythium, this is not 
because cucumbers are resistant to con¬ 
generic forms. In the course of routine 
procedure for obtaining the production 
of zoospores, for which purpose the tis¬ 
sue of cucurbitaceous fruits is not with¬ 
out merit, the writer has inoculated 
cucumbers with scores of strains having 
smooth oogonia, subspherical sporan¬ 
gia (or conidia), and fluffy aerial my¬ 
celium, belonging evidently to a num¬ 
ber of related species—in short, with 
strains of the type traditionally and no 
doubt often correctly designated in 
papers on plant diseases as Pythium 
debaryanum Hesse. These strains have 
been isolated, for example, from the 
