38 Richards . — The Evolution of 
After an experiment was completed, the tubers were cut 
in pieces and examined for any decayed spots. The surfaces 
of the wounds made in the potatoes never showed any signs 
of decay, presenting only the layer of corky tissue, quite 
dry and hard, over the surface. 
The highest maximum ever noted was a temperature- 
difference of the injured and uninjured potatoes of almost 
0-4° C. The return to the normal temperature after the 
maximum is slower than the ascending curve. There is 
a distinct drop in the temperature a few hours after the 
maximum, followed by a much slower decrease ; until, by 
the fourth or fifth day after the injury was inflicted, no 
difference was to be determined with the apparatus used. 
The actual rise in temperature is not, of course, so very much ; 
but when the normal temperature of potatoes in relation to 
the surrounding medium is considered, it is not to be despised. 
Repeated experiments showed that at the temperature of the 
warm room, namely about 24 0 C., old potatoes of the previous 
year showed a difference between the living and dead tissue 
of o-i6° C. In new potatoes only recently out of the ground, 
the plus temperature under the same conditions of temperature 
and moisture was somewhat lower, viz. 0-13° C. That the 
old potatoes have a higher temperature than the new ones 
is not remarkable, since the former are just emerging from 
their resting period, while the latter are just entering a period 
of quiescence where the metabolic activity is naturally low. 
A similar difference was found in the reaction to injury where 
the young potatoes did not respond so actively to the 
stimulation of the wound (compare Expts. 7, 9, and 10). 
The relation which the rise of temperature bears to the 
increased respiratory activity after injury is naturally not to 
be directly estimated ; since in this case the local warmth 
only is measured, while in the experiments on respiration it 
was the total effect which was determined. Approximately 
speaking, the temperature directly on the surface of a wound, 
or just below it, at the time of its maximum is about twice 
as great as the normal plus temperature of a living over 
