A Description of a Recording Porometer and a Note 
on Stomatal Behaviour during Wilting. 
BY 
C. G. P. LAIDLAW, M.A., 
AND 
R. C. KNIGHT, B.Sc. 1 
With three Figures in the Text. 
I N experiments involving the estimation of stomatal aperture it is often 
necessary to obtain a continuous record of stomatal behaviour over 
a considerable period. The necessity for making continuous observations 
by any of the usual methods is inconvenient, especially when observations of 
other phenomena have to be made. Balls ( 1 ) has used with success an 
automatic recording porometer, the Stomatograph, the chief objection 
to which is its high cost. More recently, Neilson Jones (2) has devised 
a recording porometer which can be constructed in the laboratory from 
inexpensive material. The apparatus here described is also of simple con- 
struction, and it has been found very satisfactory for stomatal investigations. 
The apparatus is essentially a self-recording modification of the 
aspirator porometer which has been described by one of us in a previous 
paper ( 3 ). In that paper it should have been stated that Balls ( 1 , p. 34) has 
experimented with a recording aspirator, which, however, was subsequently 
abandoned for the type of apparatus of his Stomatograph. 
In the present apparatus a head of water in a constant-pressure aspirator 
is employed to draw air through the leaf, and the speed of the air-stream 
(and therefore the relative size of the stomatal apertures) is measured by the 
rate at which water flows from the aspirator. 
The apparatus is shown diagrammatically in Fig. 1. A is a wide- 
mouthed bottle fitted with a rubber stopper pierced by three holes, through 
1 This work was undertaken by both authors jointly, but owing to the death of Mr. Laidlaw, who 
fell at Richebourg l’Avouee in April, 1915, the second author is alone responsible for the statements 
in the paper. 
[Annals of Botany, Vol. XXX. No. CXVII. January, 1916.] 
