57 
EUPHORBIA VI ROSA AND ALOE DIGHOTOMA 
Immediately after 10.30, the branch of the Euphorbia B was wounded in the 
usual mannei on two furrows, one of which contained the thermometer {Pi). 
The results are shewn in Table I. The main point of interest is that no 
response was observed in the unwounded stem (If). As has been suggested 
above, the explanation is no doubt to be found in the fact that If had been 
both wounded and mutilated on the previous day, whereby its pith gases 
were reduced to atmospheric pressure. It therefore furnishes an interesting 
confirmation of the hypothesis that the fall in temperature at a distance from 
the wound is due entirely to gas-expansion. 
No. 9. December 20. 
Plants. Aloe A (wounded). 
Aloe B (control). 
Thermometers. T (in Aloe A), If (in Aloe B). 
Immediately after the midday reading, the stem of Aloe A was wounded. 
The bark was removed from an incomplete ring 1 2 inches high, so situated 
that the level of the insei’tion of the thermometer bisected its height. The 
wound included more than three-quarters of the circumference of the stem : the 
insertion of the thermometer was in the unwounded part of the ring. The 
wound exposed the secondary tissues of the wood which were wet to the 
touch. The operation of wounding was completed at 12.9. 
For 51 minutes after the completion of the wounding (i.e. until 1 p.m.) the 
curve T was not affected but continued to ascend slightly more rapidly than 
If. After 1 o’clock a marked divergence commenced, for while If continued 
to rise, T began a steady fall. Evaporation began as soon as the bark was 
removed, and its amount was so great that the surface very quickly felt cold 
when touched. The time which elapsed between the infliction of the wound 
and the first response by the centrally situated thermometer-bulb was sufficient 
to allow of the view that the fall in the internal temperature is due to con- 
duction between the interior and the surface. T fell fairly steadily till 3.30. 
After 3.30 the fall was checked and a slight rise occurred between 4.30 and 
5.30. After 6 o’clock the fall began again and was probably continued through 
the night. If meantime rose continually until it reached a maximum at 6 
o’clock and maintained it for half an hour. On December 18 (Chart II) 
If remained constant at its maximum temperature from 4.30 until 6 ; T from 
5.30 until 6. This partial recovery of T between 3.30 and 6 may therefore 
be regarded as a natural result of the external temperature conditions pre- 
vailing in its immediate locality. Its recovery also followed more or less 
closely upon the cessation of rapid evaporation at the wounded surface, for it 
was noted at 4 p.m. that “ the exposed wood now feels quite dry. 1 he arrest 
of the fall at 3.30 therefore probably indicates that equilibrium had been 
5 
A. B. H. 
