56 Laidlaw and Knight. — Description of a Recording Porometer . 
temporary opening, since severing the petiole beneath gelatine cannot cause 
more or less shock than severing it beneath water, and yet in the one case 
the opening occurs, and not in the other. 
At the same time it is shown that when the leaf does not wilt the effect 
of severing it from the plant is practically nil. 
From our experiments, therefore, it appears that when a leaf is detached 
from the plant and allowed to wilt, the stomata open for a short time before 
finally closing, and these results are quite in accordance with the observations 
of Darwin and Pertz. 
In addition, some direct evidence has been obtained in support of 
the explanation of this phenomenon offered by Darwin, viz. that it is 
the direct result of wilting probably due to the guard-cells retaining their 
turgor longer than the other epidermal cells. 
Neither stomatal closure due to shock nor the entrance of air into 
the leaf through the petiole can account for the increased porometer 
readings after detaching a leaf. 
Summary. 
1. A description is given of a modification, making it self-recording, of 
the aspirator porometer described earlier. 
2. Experiments on various plants confirm the observations of Darwin 
and Pertz — that on detaching a leaf from the plant and allowing it to wilt, 
the stomata open temporarily before finally closing. 
3. Evidence is adduced in support of Darwin’s suggestion that this 
phenomenon is due to wilting. 
Department of Plant Physiology and Pathology, 
Imperial College of Science and Technology. 
References cited. 
1. Balls, W. L. : The Stomatograph. Proc. Roy. Soc., vol. B. 85 , T 9 I3 > P- 33 - 
2 . Neilson Jones, W. : A Self-recording Porometer and Potometer. New Phytologist, vol. xiii, 
I 9 I 4 ? P- 353 - 
3 . Knight, R. C. : A Convenient Modification of the Porometer. New Phytologist, vol. xiv, 
1915, p. 212. 
4 . Darwin, F. : Observations on Stomata. Phil. Trans., vol. B. 190, 1898, p. 548. 
5 . A Self-recording Method applied to Movements of Stomata. Bot. Gaz., vol. xxxvii, 
1904, p. 89. 
6. Darwin, F., and Pertz, D. F. M. : New Method of Estimating the Aperture of Stomata. 
Proc. Roy. Soc., vol. B. 84, 1911, p. 149. 
7 . Lloyd, F. E. : Physiology of Stomata. Carnegie Institute Publications (Washington), No. 89, 
1908, p. 81. 
8. Dixon, H. H. : Transpiration and the Ascent of Sap in Plants. Macmillan’s Science Mono- 
graphs, 1914, p. 124. 
