1904] DARWIN: MOVEMENTS OF STOMATA gi 
EXPERIMENT 51, fig. 5. December 25, 1899. EUPATORIUM WEINMANNIANUM. 
An attached Eupatorium leaf on the bulb R; an attached Alisma leaf on 
the bulb B, 
12:21 Eupatorium severed ; rapid R-cool rise lasting 6 or 7 minutes, followed 
by an R-warm fall, lasting 24 minutes. 
The following experiment shows the same result occurring 
slowly in an aquatic plant, in which class the stomata, as is well 
known, close much less effectively or in some species not at all, 
as the leaves wither. 
EXPERIMENT 52, fig. 6. January 16, 1900. ALISMA. 
Attached Alisma on bulb B; withered Eupatorium on R. 
A.M. 
10:28 B-cool fall showing difference between the transpiring Alisma and the 
partially withered Eupatorium leaf, 
11:54 Alisma cut: an immediate B-cool fall showing opening of stomata, 
lasting for about half an hour, followed by gradual closure (B-warm) . 
lasting more than 3% hours. 
The following readings of the horn hygroscope show that the 
Alisma stomata were not fully shut even towards the end of the 
period of closure. In this experiment the stomata of the Eupa- 
torium leaf were not quite shut at the beginning of the experi- 
ment, though the low reading (10) of the horn hygroscope shows 
that they were nearly shut, nor were they quite shut even at 3 
p.M. The withering of the leaves of this species is, I think, 
somewhat capricious. 
READINGS WITH THE HORN HYGROSCOPE, 
A.M. Alisma Eupatorium Difference 
11°53 f “ . 3 
it? s4° - -- = Cut Alisma. 
11:56 - - - 40 I a", 
T2723. - us - 40 9 31 
12:42 - . - 35 9 26 
P.M. 
Pre G Gane - - ei 4." 8 17 
mee - - - 22 7 (avg. of 2) 15 
3:00 : 
The difference between the horn hygroscope readings of the 
two leaves is given in the dotted line (fig. 6) and agrees fairly 
with the temperature curve. 
