Aug. i, 1921 
Wound-Cork Formation in the Sweet Potato 645 
in the sweet-potato storage house at a temperature of about 20° to 25 0 . 
Some potatoes were taken from the storage house at the time the experi¬ 
ment was set up, cut in halves, and the cut surfaces also smeared with the 
spore suspension. Table IV shows the results obtained as indicated by 
the final observations taken after 18 days. 
Table; IV. —Efficiency of the healed surface in preventing decay of sweet potatoes by 
Rhizopus 
In incubator. 
In storage house. 
Treatment. 
Number 
Number 
Percent¬ 
Number 
Number 
Percent¬ 
of halves 
of halves 
age 
of halves 
of halves 
age 
decayed. 
healthy. 
decayed. 
decayed. 
healthy. 
decayed. 
Healed. 
O 
35 
5 
a 
54 
12 
T Q 
Healed surface removed. 
9 
u 
64 
1 
I, 0 
Freshly cut potatoes from 
4 
2 5 
storage house... 
8 
6 
57 
16 
80 
4 
The data contained in Table IV show that under the conditions of 
this experiment the healed surface formed a very efficient barrier to 
infection. In the incubator none of the healed potatoes decayed. On 
the other hand, 64 and 57 per cent, respectively, of those from which the 
healed surface had been removed and the potatoes which were freshly 
cut decayed. Somewhat similar results were obtained with potatoes 
held in the storage house. However, in this instance one healed specimen 
decayed, while 25 and 80 per cent, respectively, of the unhealed halves 
rotted. Since the conditions of this experiment more nearly approach 
those to which wounded potatoes are normally subjected, there seems 
to be little doubt that the healed surface forms a quite effective barrier 
against the attack of microorganisms. This is further substantiated by 
other experiments which are recorded below. 
In one experiment 11 potatoes which were injured at digging time and 
had formed a hard protective covering over the wounds were used. 
A Van Tieghem cell was sealed upon the injured surface with vaseline. 
A 24-hour-old culture of Rhizopus tritici in sweet-potato decoction was 
poured into this cell and the top covered with a cover slip to prevent 
evaporation. The potatoes were held in a moist chamber at room tern- 
perature. In no case did any rot occur. 
A similar experiment was conducted in which the potatoes used had 
been cut and held in a constant-temperature chamber at a high relative 
humidity for about 3 weeks. Sections through the cut surface did not 
show a definite cork layer, but a subserization of some of the cell walls 
had taken place, as was denoted bj^ their reaction to iodin green. Four 
halves were used in this experiment, and in no case did any rot take 
place. Four other potatoes from this same lot were inoculated in the 
side opposite the cut surface by the ordinary well method. These were 
