56 
INTERNAL TEMPERATURES OF 
16 minutes. Then commenced a slow recovery which was interrupted by the 
infliction of a second wound at 10 A.M. (see No. 7). The thermometer Iv was 
not read between 9.30 and 9.37 ; in the interval it fell l 0- 25 C. In the suc- 
ceeding 2 minutes it fell a further 0 o- 25 C. after which it made a jerky 
recovery until 9.53, from thence remaining stationary until 10 o’clock. In 
the wounded stem W the cooling effects of evaporating latex are practically 
excluded. The fall of 0 o- 75 C. should therefore be due entirely to the 
sudden expansion of pith gases made possible by the removal of the top of the 
stem. If the whole fall in temperature recorded by Iv (viz. l 0- 5 C.) is also 
due to gas-expansion we have the peculiar result which has been observed 
before, viz. that the effect at a greater distance from the wound is greater 
than at a nearer point (see No. 3). 
The removal of the top of the stem of W had to some extent exhausted 
the available supply of latex. It seemed therefore that a second wound 
inflicted on W would throw further light upon the influence of surface- 
evaporation. 
No. 7. Immediately after the 10 o’clock reading, the stem W was again 
wounded, this time in accordance with the practice of previous days, viz. the 
surface of the furrow containing the thermometer was scored by two crossed 
series of diagonal cuts for about 1 inch above and 1 inch below the position 
of the thermometer. At 10 o’clock W was still rising ; BB was rising very 
rapidly. After the wounding very little latex exuded. The temperature of 
W shewed no fall but remained stationary for 14 minutes; in the 16 minutes 
immediately following it rose 1 °'7 5 C. As in the preceding case, so here, the 
effect of the wound seems to have been felt to a greater extent in the un- 
wounded branch Iv than in the one on which the wound was made. Iv was 
not read between 10 and 10.4, but in that interval its temperature fell 0°’25 C. 
and in the next 4 minutes it dropped a further 0°'25 C. 
In this case, the causes which are assumed to bring about the total fall of 
temperature at the wound have been greatly reduced, one of them probably 
removed entirely. The mutilation of the stem W earlier in the day has probably 
reduced the gas-pressure in its vicinity to that of the atmosphere ; expansion 
therefore does not occur as a result of the second wound. The partial ex- 
haustion of the latex ip the previous wounding prevents a copious outflow 
after the infliction of the second wound. So much as does exude is mainly 
drawn from the more distant parts of the plant — hence the fall, due to 
expansion, at Iv and the arrest, due to surface-evaporation, at W. 
No. 8. December 17. 
Plant. Euphorbia B. 
Thermometers. Iv and W in the same positions as in Experiment 7. 
The thermometers were in the same positions as on December 16. 
