Aug. i, 1921 
Wound-Cork Formation in the Sweet Potato 643 
tions will almost invariably decay by this organism. It was thought 
that perhaps these studies might show some correlation between the cork 
formation and the susceptibility of the potatoes to decay. Consequently, 
experiments were designed to test the resistance of the potato to infection 
through wounds which had been allowed to heal for different lengths of 
time. In these experiments potatoes were cut in two parts and placed 
in a moist chamber. After they had healed for a definite length of time 
a fresh cut was made in one half, which was to serve as a control. Both 
halves were then inoculated, and the results were noted. The “well” 
method described by Harter, Weimer, and Adams (3) was used in most 
of the experiments described below. In these cases a hole was made into 
the cut half of the potato with a cork borer at the time the experiment was 
started and a similar hole was made in the control half on the day the 
inoculations were made. In other cases the method was slightly modi¬ 
fied, in that a hole was made in the cut surface of the potato with a 
knife and a similar hole in the control later. In both of these cases the 
inoculations were made by pouring into the cavities a 24-hour-old cul¬ 
ture of Rhizopus tritici in about 5 cc. of sweet-potato decoction. About 
half of the mycelial growth formed by this organism growing on sweet- 
potato decoction in a 150-cc. Erlenmeyer flask was placed in some 
instances upon the flat cut surface of one half of a potato which had 
healed for a certain number of days and the remainder on the other 
half, the control, from which a slice about % cm. thick parallel to (he 
wounded surface was first removed. 
In general, the results shown in Table III indicate that the cork layer 
does possess some power to prevent infection by Rhizopus, but in the 
majority of cases under the conditions of these experiments infection is 
only retarded. The method used is subject to criticism in that the test 
was an extreme one, since a large amount of very active hypliae and 
enzym was placed in contact with the healed surfaces. Such conditions 
would never be duplicated in nature, and probably the cork layer would 
never be required to withstand such a rigid test under natural conditions. 
However, as pointed out above, attempts to infect even a freshly cut 
potato with dry spores or hyphae almost always fail. It was necessary, 
therefore, to use some method whereby infection of the control could be 
obtained with certainty. 
The last column in the table shows those instances where a cork layer 
was actually demonstrated to be present by free-hand sections. 
It was pointed out above that a cork layer did not form so readily about 
the base of a wound made by striking a potato against a dull instrument. 
Although no attempt was made to determine the rate of cork formation 
about the base of the “well,” it seems reasonable to suspect that it might 
not develop at a uniform rate in all places. In that case these tests of 
course would not necessarily indicate the true value of healing as it might 
