37 
Heat by Wounded Plants. 
perimented with them in regard to their respiration in the 
injured condition, and it was desirable to be able to compare 
the results of this with those of the previous investigation. 
The experiments with potatoes will, then, be first taken up. 
It was never found that there was any difference in tempera- 
ture between the cut surfaces and the uninjured potato 
immediately after injury; it was not until the second obser- 
vation was made, usually some two hours after wounding, 
that any indication of increasing warmth in the injured plant 
was noticeable. The amount of increase was not found to be 
great at this time, being only about 0 * 07 ° C., but there is a 
steady increase after this. That there should be no sudden 
increase immediately after injury is to be expected. The 
cause of the large C0 2 -production at this time has been 
shown 1 to be a physical one. The maximum temperature is 
not reached until some twenty-four hours after injury, a period 
corresponding to that of the respiration-intensity. As might 
be expected, there is some range of variation in the reaction 
of individual potatoes. Many things might lead to differences : 
as, for instance, a difference in the metabolic activity due to 
different age. It was usually found, however, that potatoes 
procured at the same time, i.e. which had presumably been 
gathered simultaneously and kept under the same conditions, 
gave pretty uniform results. The difference between old 
potatoes of the previous year and new ones was marked, as 
will be discussed a little later. One source of error which 
was to be guarded against was the use of unhealthy potatoes. 
It was found that sometimes potatoes with only a small 
rotten spot, which had no influence on the general temperature 
of the tuber, would further rot in the warm, moist atmosphere 
in which they were kept, until the decayed portion would 
affect the temperature of almost the whole potato. This is 
particularly insidious in that the increase of temperature from 
the rotting of the potato would simulate the rise following 
injury. Several series were discarded for this reason, and 
great care was taken to have none but healthy potatoes. 
1 Richards, Respiration of Wounded Plants, Ann. Botany, Vol. x, p. 544, 1896. 
