2 36 Knight . — The Interrelations of Stomatal Aperture , 
Experiments were carried out in the usual manner, records being 
made of stomatal aperture, transpiration, absorption, and the evaporating 
power of the air. The last was merely a check upon the constancy of the 
atmospheric conditions, and experiments in which it was irregular were 
discarded. 
The results showed the same tendency as before, an excess of absorp- 
tion over transpiration producing an increase in the latter, and vice versa. 
When the transpiration rate of a plant had been reduced by the lack of 
water it was found possible, by decreasing the evaporating power of the air, 
to reduce the transpiration rate below the rate of absorption and allow 
some of the water deficit to be made up. Then, on increasing the evaporating 
power of the air to its original value, it was found that the transpiration 
rate had increased with the increased water-content. An example of this 
is given below. 
Experiment 46. A shoot of Eupatorium adenophorum was cut from 
a plant which had been in the dark room over night and was mounted in 
the usual way. The records showed that the rate of transpiration was 
greater than the rate of absorption and therefore that the water-content of 
the plant was decreasing, the transpiration rate falling at the same time. 
The evaporating power of the air was then reduced in the ratio of about 1 *6 
to i*o by stopping the fan in the air-flue. This reduced the transpiration 
rate still further, and it was now well below the rate of absorption and the 
water-content of the plant increased. The fan was started again at its 
original speed after a half-hour period of ‘ still air *, to determine the rate 
of transpiration with increased water-content. The results are given in 
Table IV and Fig. 4 . 
Table IV. 
No air movement during period 3.30-4.0 p.m. 
Plant. Stomata . 
Half-hour 
At mo meter 
Transpira- 
Absorption 
Time. 
Stomatal 
periods 
water loss 
tion in 
in mg. 
aperture. 
ending 
in mg. {E). 
mg. ( 7 ). 
11.452 
i.m. 
1 60 
12.30 
p.m. 
222 
518 
330 
12.15; 
p.m. 
173 
1.0 
>> 
218 
440 
39 ° 
12.45 
a 
187 
1.30 
i) 
220 
395 
330 
1. 15 
a 
186 
2.0 
}» 
218 
405 
410 
i -45 
a 
182 
2.30 
i) 
222 
400 
380 
2.15 
a 
189 
3.0 
ii 
220 
402 
400 
2 -45 
a 
188 
3.30 
it 
220 
416 
380 
3 -i 5 
n 
183 
4.0 
it 
135 
337 
420 
3-45 
a 
188 
4-30 
» 
225 
465 
390 
4.15 
a 
190 
5.0 
)i 
225 
447 
420 
4-45 
a 
192 
5-30 
it 
222 
438 
400 
5 -i 5 
a 
196 
Total 4663 4250 
Decrease of water- content of plant, 413 mg. 
