1904 } DARWIN: MOVEMENTS OF STOMATA 93 
and not a direct specialized reaction of the stomata to dryness 
of the air. I undertook these experiments in consequence of 
reading Aloi’s papers,’? with which I was unacquainted when I 
wrote my Observations on stomata. The point of Aloi’s work is 
his proof that leaves exposed to a very dry atmosphere may have 
widely opened stomata, if the plants are well watered. 
My experiments were carried out as follows: A plant is placed 
under a water-sealed bell jar, z.¢., in a very moist atmosphere. 
14 
14 ae ce | 
18 ro! tae ae dew 
A= 
2 
4 -f 
6 1 eal os = 
- i238. ‘ y 
4 Ne fs 
9 92 ba 
Oo 
= — 
“ aoe cea 
< _¢ = 
a i  & 
a] _ 
A a Re 
. — 
\ : EERE 
he SS SS Ss ee ee 
| 
~ . 4 Y 
= & 3 B 3 
2° = Se Pr 
Fic. 6.—See Experiment 52, p. 91. 
The bell is removed, and a reading with the horn hygroscope 
taken at once; the plant is then left in the dry air of a room, 
and it is found that the stomata gradually close, in spite of the 
illumination remaining practically unchanged. This is the class 
of experiment recorded in Odservations on stomata. The new 
fact brought to my notice is that the result often fails with plants 
growing in well-watered soil, while it succeeds more uniformly 
with plants in which the soil is dry. This points to the conclu- 
sion that the closure of the stomata depends on the loss of water 
in the plant as a whole being greater than the intake. Analogous 
*° ALol, La traspirazione delle pianti terrestri, etc. Catania, 1891. ALOIL, Influ- 
enza dell’ umidita del suolo sulla traspirazione, etc. Naturalista Siciliano 13: —- 
(Ni. 4-9.) 
