Porometer in Stomatal Investigation . 61 
cation of the stimulus. Such an effect may be the result of forcing apart 
resilient guard-cell walls which return to their original conformation imme- 
diately the rush of air ceases. By the porometer method it is obviously 
impossible to detect such an error, and equally impossible to avoid it, 
but the existence of any large error of its kind seems unlikely. 
(3) In view of the fact that a porometer experiment involves the 
attachment of the leaf-chamber to the leaf by means of some adhesive, 
a somewhat violent treatment, some experiments were carried out to obtain 
some indication of the response, if any, of the stomata to shock. 
In some experiments, in another connexion, it was observed that 
vaselining the upper surface of a leaf of Acalypha Wilkesiana var. mar - 
ginata with a brush caused rapid closure of the stomata, which are con- 
fined to the lower surface. This was attributed to shock, but the 
experiments were not followed up. 
In later experiments it was frequently noticed that shortly after 
fixing the chamber to the leaf, the size of the stomatal apertures, from 
porometer readings, was much less than, in the light of later readings 
from the same portion of leaf, seemed consistent with the general con- 
ditions of atmosphere and illumination. It was thought that, possibly, this 
was due to the fact that the manipulation necessary for the attachment of 
the chamber to the leaf caused the stomata to close. Confirmation of this 
was sought in a series of experiments, all of which gave the same results ; 
one of which is given in detail below. 
Expt. 56. 15. xii. ’14, and 16. xii. ’14. 
The plant used was Eucharis Master si, and at 2.0 p.m. on 15. xii. T4 
two similar leaf-chambers, B and D, were fixed to different parts of the same 
leaf. Readings were taken at intervals from 2.30 p.m. onwards, and showed 
that the stomata opened rapidly until about 3.30 p.m., when they began to 
close, doubtless owing to the failing light (see Fig. 3). The readings were 
continued the next morning and throughout the day. At 11.35 a * m * another 
chamber, c, was attached to the leaf and readings taken from it as from the 
others. The most important point revealed in the resulting curves is that 
the stomata at C were at 13.10 p.m. almost closed, but they rapidly opened 
to a maximum at 1.30 p.m. at the same time as B and D, finally closing in 
unison with them. 
It may be assumed that the stomata at C behaved similarly to those at 
B and D on the morning of 16. xii. T4, and that at 11.35 a>m * t^ e y were 
fairly widely open, but that they closed in response to the shock sustained 
in fixing the chamber C, but recovered by 1.30 p.m. The same conclusion 
applies to the closed state of the stomata at B and D at 3.30 p.m. on 
15. xii. T4. 
1 N.B. — The reason for lack of absolute coincidence, even under practically identical conditions, 
between b and d is discussed in a later section of this paper. 
