1304 * 
A great advantage of this method is, that the values found are 
not directly connected with the transpiration...” 
“An advantage offered by the porometer-method above all other 
methods is, that it enables us to examine the stomata in the living 
leaf, which remains attached to the plant, in circumstances more 
normal than with the other methods. It enables us to observe the 
same leaf a very long time consecutively without ifs experiencing 
any injurious consequences”. 
Finally van SLOGTEREN ') points out, that the porometer of DARWIN 
and Prrrz should also be preferred, because it likewise indicates 
small modifications in the aperture accurately and makes known 
the average of thousands of stomata at the same time. 
It might be expected, that after the method of Darwin and Prrtz’) 
got known, attempts should be made, to make it capable of self- 
recording. It may be said, that the phenomenon to be studied asks 
for a continuous picture projected of its changes. Indeed some three 
self-recording porometers have already been described (resp. by 
Batis?), Jones *) and Lawnaw & Kuient *) of whieh Barrs's stoma- 
tograph may be called the most successful. About these apparatus 
VAN SLOGTEREN says‘): “There is a danger, that either a too great 
pressure is used, or the apparatus is made so complicated that it 
may give rise to all kinds of sources of error. A great advantage 
of the original porometer of Darwin and Perrz is its very simplicity, 
through which the influence of external factors exercised on the 
apparatus, is so easily judged. Besides the plant is placed in quite 
abnormal circumstances, if a continuous current of air is sucked 
through the leaf, as is necessary in these methods”. 
With the recording porometer, that Lam now going to describe, all 
these objections have been avoided and the circumstances in which 
the plant remains during the experiment, are even more favourable 
than in the case of the original porometer. 
§ 2. General description. 
When a selfrecording apparatus is made, the purpose is a.o. to 
Dele psa: 
2) F, DARWIN and D. F. M. Pertz. On a New Method of Estimating the 
Aperture of Stomata, Proc. Roy. Soc. Lond Serie B, Vol. 84, 1912. 
3) W. L. Batis, The Stomatograph, Proc. Roy. Soc. Lond. B, 85, 1912, p. 33. 
4) W. NeiLsoN Jones, A Selfrecording Porometer and Potometer, New Phytologist, 
XIII, 1914, p. 353. 
5) CG. G. P. Larpvaw and R. C. Knieur, A Description of a Recording Poro- 
meter etc., Annals of Botany, XXX, 1916, p. 47. 
Gen pt 6: 
