642 
Journal of Agricultural Research 
Vol. XXI, No. 9 
10 days to 2 weeks when first placed in storage by subjecting them to 
a temperature of about 25 0 to 30°. This is likewise the most favor¬ 
able temperature for periderm formation. Experiments previously re¬ 
corded showed that in those particular instances no cork was formed 
preceding or during the curing period. In all probability the relative 
humidity was the inhibiting factor. Similar experiments conducted at 
intervals of about 2 months throughout the season showed that at no 
time were the potatoes able to form a cork layer over a cut surface under 
storage-house conditions. However, controls held in moist chambers 
in the laboratory at the same time never failed to do so. 
Although no periderm formed beneath cut surfaces under storage- 
house conditions, a cork layer was laid down just beneath dead rootlets. 
Likewise a similar layer of cells was laid down just beneath the wound 
made by breaking the potato from the roots. In the former case the 
dead rootlets probably served to prevent a too rapid drying of the 
wound, and a cork layer was formed. Likewise the deposit of the latex 
over the wounded end of a freshly dug sweet potato probably forms a 
protection against the escape of moisture, which may explain in part at 
least the formation of a cork layer under such conditions. 
Sweet potatoes which have sprouted either in the hotbed or in the 
storage house have the power to form a cork layer when placed under 
suitable conditions. Some sweet potatoes with soft and flabby ends 
were placed in moist chambers in an attempt to learn whether they 
would form a cork layer. In most cases, however, the exposed tissues 
at the dried end soon turned brown and began to decay. This would 
seem to indicate that sweet potatoes lose their power to form a protec¬ 
tive covering over their wounds when they once become badly shriveled, 
the degree of drying being the deciding factor. It has been demon¬ 
strated also ( 12 ) that sprouted Irish potatoes form a new cork over 
wounds, but that drying of the tissues, which usually accompanies ger¬ 
mination when potatoes are stored in a warm room for a long time, 
retarded it. 
The skin of the sweet potato, as well as that of the Irish potato (n), 
serves as an effective protection against the death of the tissues beneath 
by desiccation and from the attack of microorganisms. When this is 
broken the exposed cells would soon die were it not for their power to 
form some sort of protective covering. Incidentally this protective 
layer may possibly, at least to some extent, serve to prevent infection 
by microorganisms. 
EFFICIENCY OF THE WOUND CORK IN PREVENTING INFECTION 
The writers have nearly always failed to produce infection in sweet 
potatoes by Rhizopus by smearing spores and hyphae over a freshly cut 
surface. Nevertheless, wounded potatoes subjected to certain condi- 
