PICTURESQUE EXPERIMENTS 213 



Porometer. Its essential part is shown in Fig. 7. 

 It consists of a funnel-shaped tube, having a broad 

 flange, which is cemented on to the stomata-bearing 

 surface of a leaf. The leaf is represented by the 

 obliquely shaded object and is enormously magni- 

 fied. To the upper orifice of the funnel is fixed a 

 rubber tube, and by means of it steady suction 

 can be supplied. The result is that a current of air 

 is drawn through the stomata into the leaf, and 



Fig. 8. 

 Curve of Porometer readings in light and darkness (black). 



then out of the leaf into the cavity of the poro- 

 meter. The rate of this current is an index of the 

 degree to which the stomata are open. With this 

 apparatus a number of interesting points can be 

 determined. 



Fig. 8 shows the effect of alternate periods of 

 light and darkness. The fall of the curve represents 



