7i5 
the Respiratory Exchanges of Leaves 
Miss Irving, who determined the rate of production of C 0 2 from the 
first moment of exposure, has shown that the first effect, even of large 
concentrations of vapour, is to stimulate the production of C 0 2 ; this effect 
becomes more intense and more shortlived the more the dose is increased, 
until it may be described as a transient outburst of C 0 2 . In my experi- 
ments this brief stimulation was seldom observed, as it took place in the 
chloroforming vessel before the measurement of the gaseous exchange could 
be begun. When a detailed collation is attempted, however, it appears 
probable that the intensity and duration of the augmented output of C 0 2 
shown in Miss Irving’s experiments, depends in some degree upon the con- 
tinuance of the exposure to chloroform vapour. This is well brought out if 
Miss Irving’s Experiment XIII 1 and my Experiment IV 2 are compared. 
In her experiment leaves of Cherry Laurel were exposed continuously to 
the vapour of 0-63 c.c. of chloroform per litre of air ; in mine, similar leaves 
were exposed for twenty minutes to the vapour of 0-5 c.c. per litre. The dose 
was rather smaller in my experiment, yet whereas in it the production of 
C 0 2 was far below normal from the first (i. e. from less than half an hour 
after the first moment of exposure, onwards), in Miss Irving’s experiment it 
was increased nearly threefold, and was still above normal in the fourth 
hour, though rapidly diminishing. Only with much larger doses was the 
outburst over in half an hour under continued exposure to chloroform. 
It seems improbable that the difference of temperature (18*5° in mine, and 
25 0 in Miss Irving’s) could account for such a difference, and the inference is 
suggested that this exaggerated production of C 0 2 only lasts so long as the 
leaf remains exposed to chloroform vapour, or dies away with great rapidity 
as soon as no more chloroform is administered. 
When, on the other hand, the concentration of chloroform is low, the 
smaller acceleration then produced dies away more slowly after exposure 
to chloroform ceases : this more persistent stimulation appears, therefore, 
also as an after effect. Here again, however, if exposure is repeated, 
a similar stimulation is again produced, as in Experiment XII with 
Tropaeolum ; 3 while continuous exposure intensifies and prolongs the 
stimulation, or may lead to disorganization. 
There are many points which still require elucidation. One of the 
most interesting is the relation between the respiratory exchanges and 
changes of permeability. Lepeschkin 4 showed that the exudation of 
water from the sporangiophore of Pilobolus can be diminished by a small 
dose of chloroform gradually applied, indicating a decrease of permeability, 
whereas a large dose increased the permeability. Recently Osterhout 6 has 
found that 1 per cent, ether or 0.05 per cent, chloroform in sea-water pro- 
1 Loc. cit., p. 1089, Fig. 15. 2 p. 7 03. 
4 Beihefte z. Bot. Centralbl., xix, Abt. I, 1906, pp. 416-17. 
6 Science, N. S., xxxvii, 1913, p. ill. 
3 p. 711. 
