Parameter and a Note on Stomatal Behaviour during Wilting. 5 1 
per thirty seconds to about one drop per 120 seconds. In work with 
plants, the rate can be arranged by selection of the leaf- chamber and regula- 
tion of the pressure difference in the aspirator. Naturally, owing to stomatal 
changes, the rate changes considerably during a day, and very slow rates are 
unavoidable, but for short experiments in daylight the above-mentioned 
speeds have been found easy to arrange. 
The experiments with fine capillaries and punctured platinum discs 
gave indications of the existence of a rhythm in the flow of air, and although 
it was realized that some of the observed irregularities might be due to the 
capillaries themselves, attempts were made both to determine and to elimi- 
nate this rhythm. It was thought to be due to the small pressure changes 
resulting from the relative sizes of the drop at E and the bubble at B, 
and various combinations of sizes of these two tubes were tried, but failed to 
give satisfactory results. As the period of the rhythm probably changes 
with temperature and rate of flow, attempts to calculate it were given 
up, especially as the later experiments upon stomata gave sufficient accuracy 
without allowing for a rhythm. 
It was evident, however, that the disturbing influence of the rhythm was 
less noticeable with large than with small pressure differences, so that in so 
far as is compatible with other conditions of the experiment, it is advisable 
to employ large pressure differences; from 5 to 15 centimetres have been 
found convenient. 
By taking the precautions outlined above, it has been found possible to 
obtain very satisfactory results with the apparatus: thus, on July 2, 1914, 
with the apparatus attached to a fine capillary tube and a pressure difference 
of 10 cm., a record running for two hours gave an average distance travelled 
by the drum during the formation of one drop of 5*0 divisions of the paper 
used (= about 55 sec.), the maximum distance for any drop being 5*2 
divisions and the minimum 4-8. Typical records obtained with stomata are 
given in the second part of this paper. Test experiments have also been 
carried out to compare the records obtained with the apparatus with that 
obtained with the ordinary porometer by stop-watch readings, of which the 
following is typical : 
Exp. no. Five leaf-chambers were attached to one leaf of Maranta 
coccinea , var . floribunda at 4.30 p.m. on March 4, 1915. At 11.15 a.m. the 
next day, two were connected to two recording porometers, and the other 
three by means of a 4-way tube to a single bubbling aspirator for stop-watch 
readings ( 3 ), which were taken every fifteen minutes. The results are shown 
in Fig. 2, where the reciprocals of the distances between the two succes- 
sive marks on the drum and the reciprocals of the stop-watch readings are 
plotted against time. The recorders of course gave continuous records, but 
as each curve would involve about 350 points, only one point for each five 
minutes period is given. It has been shown in some work which it is 
E 2 
