June 1, 1925 
The Cottony Leak of Cucumbers 
1041 
stems of cucumber plants affected with 
the trouble described by Atkinson (1) 
as canker; from diseased roots of her¬ 
baceous hosts, including garden peas, 
sweet peas ( Lathyrus odoratus L.), rhu¬ 
barb ( Rheum rhaponticum L.), sweet 
potatoes ( Ipomoea batatas Poir), cress 
(Lepidium sativum L.), and spinach 
(.Spinacea oleracea L.); from roots of 
diseased seedlings of woody plants like 
Pinus ponderosa Dough, P. banksiana 
Lamb., P. sylvestris L., P. aristata 
Engelm., and Picea sitchensis Trautv.; 
and from rose, pear, and geranium cut¬ 
tings which had become diseased after 
being put in propagation beds. With 
relatively infrequent exceptions, the 
inoculated cucumber was attacked and 
the tissue invaded in much the same 
way as when Pythium aphanidermatum 
was employed, the rate of destruction 
for some forms being about equally 
rapid, while in the case of others ad¬ 
vance was slower. All of the strains of 
Pythium isolated from separate lots of 
“ leaky ” potatoes and made available 
to the writer through the courtesy of 
G. K. K. Link have proved uniformly 
destructive, as have also about a dozen 
similar strains of the P. debaryanum 
type isolated from watermelons affected 
with a decay not readily distinguishable 
from the buff blossom end-rot due to 
P. aphanidermatum . 
Although the several species of 
Pythium with subspherical sporangia 
(or conidia) and smooth oogonia show 
certain minor differences, in that some 
bring about greater softness in affected 
tissues, or a more watery condition 
than others, their effect in the interior 
of cucumber fruit is markedly similar 
to that produced by the parasite iso¬ 
lated from naturally infected material. 
The much more profuse development 
of aerial mycelium nevertheless pro¬ 
vides a conspicuous characteristic by 
which attack by Pythium aphanider¬ 
matum can be distinguished from attack 
by the congeneric species that have been 
tried out. This feature appears suffi¬ 
ciently distinctive to merit attention in 
considering a common name for the 
disease under consideration. The term 
“cottony leak,” descriptive of the most 
obvious symptoms of the malady, is 
proposed in this connection. 
In its copious extramatrical develop¬ 
ment, moreover, is apparently to be 
found the characteristic to which 
Pythium aphanidermatum owes much 
of its destructiveness to cucumbers 
when packed as in commercial con¬ 
tainers. The aerial mycelium of an 
individual fruit bearing an original 
infection grows out between adjacent 
fruits, partially or completely investing 
them. Laboratory experiments leave 
no room for doubt that such investment 
results in the infection of cucumbers, 
immediately if the epidermis is wounded, 
but without any considerable delay 
even if the epidermis is, as far as can be 
ascertained, altogether free of wounds. 
With the infection communicated from 
one . fruit to another, each infected 
specimen gives rise in the course of 5 to 
10 days to a “nest” of decaying cucum¬ 
bers, including perhaps from a dozen to 
a score of individuals. Other species 
of Pythium with relatively feeble ex¬ 
tramatrical development under condi¬ 
tions of only moderate humidity, such 
as generally prevail in produce cars, 
fail of passage from fruit to fruit, at 
least within reasonable periods of time. 
It is thus possible that if losses due to 
such species occur, the restriction of 
infection to single individuals might 
have occasioned their being overlooked 
by inspectors and others concerned in 
the examination and handling of food 
products. 
In addition to cucumbers, the patty¬ 
pan squash, the summer crookneck 
squash, as well as the more delicate- 
skinned specimens of vegetable-marrow 
squash, have proved subject to infection 
by contact or investment with extra¬ 
matrical mycelium of Pythium aphani¬ 
dermatum. In cucurbitaceous fruits 
having a rind of indurated tissue like the 
watermelon, the cassaba, the honeydew 
melon, and the muskmelon, attempts 
at inoculation by means of surface 
contact have not given positive results. 
It has been mentioned that some of 
the forms usually assigned to Pythium 
debaryanum , comprising, however, a 
relatively small minority, have failed 
to attack cucumbers when inoculated 
into incisions. A species not yet iden¬ 
tified, provided with lobulate sporangia 
and hence closely related to but not 
identical with P. aphanidermatum , 
which was isolated from diseased corn 
roots, has shown no evidence of patho¬ 
genicity on cucumber fruit. The same 
statement holds true also of the two 
species with spiny oogonia (Artotrogus) 
responsible for the widespread chocolate 
blossom-end decay of watermelons, 
strains of these forms isolated from fruit 
thus affected as well as from pear cut¬ 
tings, sweet-potato rootlets, and pea 
rootlets proving equally ineffective in 
producing decay of cucumbers. A third 
spiny species, in which the considerably 
larger oogonia are regularly borne on 
lateral branches, the swollen, somewhat 
contorted distal portion of which appar¬ 
ently serves as an intercalary antherid- 
ium, isolated only once from moribund 
rhubarb buds, similarly proved innocu- 
