100 BOTANICAL GAZETTE [FEBRUARY 
1:24 Sudden change, indicating a rise of temperature in B or fall in R, 
and as there is no reason to suppose that any change in R had 
taken place, the rise in the curve must be due to the closure of the 
ae B stomata in the drier air of the greenhouse. 
12:31 Plant B again placed in damp air. 
1:29 Leaf B again placed on pyrometer B. Again the curve indicates 
that the stomata were more open and rapidly close in dry air. The 
opening of the stomata in the damp, and the closure in the dry 
air, was observed in this experiment by means of the horn hygro- 
scope, and these approximately follow the temperature curve. 
The above results were confirmed by two more observations 
on the same Tropaeolum plants. In both cases the stomata of a 
leaf on the unwatered pot B were opened by damp air. Judging 
by the temperature curve only, in one case the dry air produced 
rapid and striking closure, in the other, slow and less obvious 
closure. 
These experiments are not thoroughly satisfactory, since both 
the well watered and unwatered plants should have been exposed 
to alternations of dry and damp air; but they show at any rate 
a degree of sensitiveness to such changes in the unwatered plant 
which I have not observed in normal plants. 
COMPRESSION OF THE STEM. 
It is known™ that compressing the stem in a vise checks the 
transpiration current. And I have shown” that the checked 
water supply produces closure of the stomata, which apparently 
reopen when the vise is unscrewed. The following is a tempera- 
ture record of the same experiment: 
EXPERIMENT 97, fig. 7}. August 23, sate 
CBEMATIS MONTANA. 
A branch placed with the cut end j in wate 
A.M, 
10:23 A leaf on bulb B, an artificial leaf on R. 
10:49 Vise screwed tightly to branch below the leaf. 
e first effect is a B-cool move, indicatin 
observed (oc. cit.) with the 
closure of the stomata (B-warm 
g the preliminary opening 
horn hygroscope; followed by 4 
). 
** DARWIN, FRANCIS, and PHILLIPS. Proc, Cambridge Phil. Soc. 5: 364. 1886. 
2 DARWIN, FRANCIS, Observations on Stomata. Phil. Trans. Roy. Soc. London 
B 190: 555. 1898. 
