58 
INTERNAL TEMPERATURES OF 
established between the absorption of heat from without and the loss of heat 
by surface-evaporation. 
The difference between the temperatures of W and T at their maxima on 
December 18, i.e. before T was wounded, was 2° C. After wounding, on 
December 20, they differed at their maxima by 9°‘75 C., the greater difference 
in this case being apparently entirely due to the consequences of wounding. 
On the following morning (December 21) at 5 o’clock, T stood at 19°‘8 C. 
while W read 25 0, 5. T continued to fall until 9 A.M. to 19°'4, W at the same 
time reading 27°'2. After 9 o’clock both rose slowly, W faster than T. At 
2.45 P.M. when the last readings were taken, T stood at 28 0- 5, W at 37 0- 8. 
The effects of the wounding of T were therefore manifested very slowly 
and for a long period and the recovery was very gradual. Indeed, but for the 
fact that many years before, Aloe B had evidently received a more severe 
wound near the base of the trunk (see Photograph 3), it might have been 
doubted whether complete recovery was possible. In this case, however, a 
partial callus had formed, and to all appearance the tree was as vigorous as if 
it had never been wounded. 
A brief visit was paid to the locality on January 22, 1913. The wood 
exposed by the wound made on December 20 was dry and easily powdered. 
The leaves were shrivelled and most of them hanging and the plant certainly 
looked as if it was unlikely to survive. Rain had fallen in the meanwhile and 
there was no reason to suppose that its appearance was the natural result of 
prolonged drought. 
5. Discussion. 
In the Aloe, as in the Euphorbia, the infliction of a surface wound is 
followed by a lowering of the internal temperature. In the former case, the 
fall commences after a considerable interval, it is slow and it continues for 
some hours when the wound is large. It is without doubt a simple effect of 
evaporation at the surface and conduction through the water-laden tissues of 
the xylem. 
In the Euphorbia the effects of surface-wounding are much less simple. 
They are complicated by the presence of large reservoirs of gas in the pith, 
by the copious outflow of latex and by the rapid formation of a pellicle of 
rubber over the surface of the wound. Here the fall in the internal tem- 
perature is due only partially to surface-evaporation ; it is considerably 
enhanced by another cause which acts more quickly and over a much greater 
distance than surface-evaporation. This cause is believed to be the expansion 
of the gases imprisoned in the pith. 
The exudation of latex 1 implies an internal pressure higher than that of 
1 This occurs even at the time of minimum air and internal temperatures. 
