nee COOL 
WARM 
92 BOTANICAL GAZETTE [FEBRUARY 
It should be noted that the closure of the Eupatorium stomata 
would not increase but slightly diminish the long B-warm rise; 
on the other hand the fall of the curve from II $54 to. 1232448 
to a very slight degree increased by the change in the Eupatorium 
leaf during that period. 
THE EFFECT OF DRY AIR. 
Stahl? has published ex- 
periments from which he 
draws the conclusion that the 
closure of the stomata in dry 
air does not depend on the 
general diminution of the store 
of water in the leaf, but rather 
on the loss of water by the 
guard cells, which may, in his 
\ opinion, be independent of the 
general withering of the leaf. 
ae ye I have discussed this difficult 
question in my Observations, 
||| where I have tentatively given 
the theory that the guard cells 
lose turgor ‘spontaneously,” 
z.é., ‘not by simple evapora- 
‘i 
at 
een OS atl ay 
a ° 
3 S tion, but in response to 4 
mh : stimulus. And this stimulus 
Fic. 5.—See Experiment 51, p. 91. 
may be the slight flaccidity of 
the rest of the leaf.’’ This point of view, though it does not 
harmonize with Stahl’s facts, has nevertheless some probability. 
According to my view, there must be, whenever the stomata 
close, a slight, though it may be an imperceptible, general detur- 
gescence of the leaf. The repetition of certain experiments 
with the horn hygroscope confirms me in my belief that the first 
stage in the closure of the stomata is a slight general withering, 
“STAHL, Bot. Zeitung, Einige -Versuche iiber Transpiration und Assimilation. 
Bot. Zeit. 5a": 121. 1894. 
?DARWIN, FRANCIs, Observations on stomata, 
898. 
Fh. 7 . Roy. Soc. London 
B. 190: 617. 1 Er ede ee 
