1092 Irving .— The Effect of Chloroform 
C 0 2 -output from the illuminated leaf; this of course was nil with the 
normal leaf, but became considerable when chloroform was given ; if on 
darkening the C 0 2 -output rose still further, it was evidence that the power 
of assimilation had not been completely inhibited, but if it remained 
stationary then the assimilative power had been abolished. 
Single leaves of Cherry Laurel were alone used in this part of the 
work, and they were set up in the oval leaf-chamber previously mentioned. 
The experiments were all carried out in the water-bath at 25 0 C., and the 
leaf in its chamber was lighted through the glass window of the bath by 
the Keith high-pressure incandescent light. When a leaf in the dark was 
compared with a lighted leaf, its leaf-chamber was wrapped in black cloth 
and placed behind a light-screen in the same bath. 
The experimental procedure was precisely the same as in Part I, and 
the chloroform was supplied by the special tube described on p. 1084. This 
was placed in the circuit just before the C 0 2 -free air entered the leaf- 
chamber, and when two leaves, one in light and one in dark, were used 
simultaneously, it was inserted just before the stream of air was bisected. 
Then, as the two aspirators were arranged to drop at equal rates, each leaf 
received exactly half the total chloroform vapour. 
As assimilation is much more sensitive to the presence of chloroform 
than respiration, the doses used in this section are smaller than those in 
Part I. It will perhaps be best to take the experiments in order of increas¬ 
ing chloroform concentration. 
Experiment XV. Chloroform co 7 icentratio 7 i = 0*0014 c.c. per litre of 
air-curre 7 it - 1 The Cherry Laurel leaf, weighing 2*3 grms., was placed with 
its stalk in water in the oval leaf-chamber which was sealed and put in the 
bath, already at the required temperature, 25 0 C. The illuminating burner 
was then lighted, and after a preliminary of three hours, a series of two- 
hour estimations of the C 0 2 given off by the leaf was started. The first 
reading showed that the leaf was assimilating all its respiratory C 0 2 
(Fig. 17) and that none was escaping from the leaf. The chloroform 
apparatus was then placed in the circuit, left in for four hours, and then 
removed. The two C 0 2 -estimations taken during this time showed the 
immediate effect of this very minute dose of chloroform ; C 0 2 escaped from 
the leaf to the amounts of o*coo2 and 00006 grm. respectively, showing 
that assimilation of its respiratory C 0 2 by the leaf was partly inhibited. 
This effect continued after the chloroform had been removed, and the figure 
shows the subsequent output of C 0 2 ; it will be noted that although this 
fell to 0*0002 grm. it did not again reach zero by assimilation, in eight hours. 
1 The chloroform sank in the graduated tube at the rate of 0-0045 c.c. per hour, but a control with 
a tube closed at the lower end showed that 0-0031 of this was due to evaporation from the upper 
surface. Therefore, only 0.0014 c * c * chloroform filtered through each hour to the air-current. 
