Porometer and a Note on Stomatal Behaviour during Wilting. 53 
measurement, failed to find any indication of the temporary preliminary 
opening described by Darwin and Pertz. 
The recording apparatus described above seemed to adapt itself well to 
a question of this kind, and consequently experiments were undertaken 
to investigate it. 
The usual method adopted was to attach two leaf-chambers to different 
leaves of the plant to be investigated, and some hours later — generally the 
next morning — each was connected to a recording apparatus, and records 
were commenced. After an interval of an hour or more, one of the leaves 
was severed from the plant, the other being left attached to the plant to act 
as a control for temperature, humidity, and illumination changes. The 
experiment was continued, after severing one leaf, for a period determined 
by the result, and in many cases the second leaf was also severed later. 
The plants used included Maranta bicolor , M. coccinea , var . floribunda. 
Primus Laurocerasus , Eucharis Master si , Eupatoriuni adenophorum , E. 
Raffilli , Pelargonium (ivy-leaved), and Phaseolus vulgaris . 
With the exception of Eucharis Mastersi all these plants showed 
the preliminary opening described by Darwin. Only one experiment was 
carried out with the Eucharis , and it is doubtful if the leaf was appreciably 
wilted at the end of the- experiment, since the lamina is fairly fleshy and has 
a thick midrib which would hold much water, so that although no preliminary 
opening occurred in our experiment, further investigation might show that 
Eucharis is no exception. 
Fig. 3 shows the result of one of these experiments upon Phaseolus 
vulgaris . 
The time elapsing between severing the leaf from the plant and 
the opening movement of the stomata varies considerably with different 
plants and different conditions, and is apparently dependent upon the rate 
of wilting. In the case of a thin leaf which wilts quickly, the opening move- 
ment occurs very shortly after the leaf is cut from the plant, whilst in 
a thick leaf the opening may be long delayed. In the curves of stomata! 
