1911.] New Meth od of Estimating the Aperture of Stomata. 153 



increased as from unity to between 8 and 9 ; this is a much greater opening 

 than occurred with Mcotiana and a fortiori than in the experiments with 

 the horn hygroscope. When estimated by y/K the opening of the stomata 

 is from 1 to between 2 - 8 and 3, and this again is greater than anything 

 observed with the horn method. 



Another experiment with Tropasolum (October 26, 1910) is here given in 

 an abbreviated form. 



Fig. 10.— Cutting the leaf -stalk of Tropseolum. The curve 

 square root of the rate of flow. 



s constructed from the 



Experiment 60p. — Tropaeolum, October 26, 1910. 



Thus the rate of flow (E) rose as 1 : 6'5, while ^/R rose as 1 : 2-6. 



There is one difference between the results obtained with the porometer 

 and the horn hygroscope, namely, that the opening and subsequent closure 

 are completed much more rapidly with the horn. I imagine that this may 

 be due to the fact that in porometer experiments the act of withering is 

 delayed by the damp air within the chamber. 



§ 7. Conclusion. 



In the foregoing sections our aim has been to give a preliminary account 

 of the porometer and its application to the study of stomata. 



The principal merits of the method are (1) that the readings of the instru- 

 ment are dependent on the aperture of the stomata, and are therefore 



VOL. LXXXIV. — B. M 



