234 Knight . — The Interrelations of Stomatal Aperture, 
Experiment 10. The day was bright and hot, the maximum tempera- 
ture being 91-5° F. A shoot of Helianthus tuberosus was set up in the usual 
way and records of transpiration, absorption, evaporation, stomatal aperture, 
temperature, and humidity were kept. The results are shown in Table III 
and Fig. 3. 
Table III. 
The numbers in the ‘Water deficit’ column represent the excess of 
total transpiration over total absorption at the end of each period. 
Plant. — Stomata. 
Half-hour 
Atmometer 
Transpira- 
Absorption 
Water 
E 
Time. 
Stomatal 
periods 
loss in 
tion in 
in mg. 
deficit in 
aperture . 
ending 
mg. (A). 
mg. ( 7 ). 
mg. 
9-55 a-m. 
171 
10.3 
» 
239 
IO.IO 
265 
5760 
10.25 
» 
299 
10.30 a.m. 
470 
5870 
no 
12.49 
10.40 
» 
347 
6730 
10.55 
426 
11.0 „ 
580 
7100 
480 
12-24 
11. 10 
568 
11.25 
)> 
620 
11-30 » 
650 
7200 
6570 
mo 
ii-o8 
1 1.40 
>> 
620 
n -55 
,, 
408 
12.0 noon 
655 
578 o 
5330 
1560 
8-82 
12.15 P- m - 
202 
Potometer refilled at 1 2 noon 
12 -35 P- m - 
690 
4810 
4420 (?) 
1950 
6-97 
12.30 
>> 
186 
12.45 
172 
i -5 » 
640 
3750 
376 o 
1940 
5.86 
1.0 
V 
154 
600 
0 
00 
00 
1. 15 
>> 
131 
i -35 » 
3270 
3330 
5*45 
1.30 
J) 
121 
i -45 
Ji 3 
2-5 „ 
545 
2860 
3090 
1650 
5-23 
2.0 
» 
114 
The stomata in this case did not begin to close till 11.40 a.m., by which 
time the water-content of the plant had decreased by i*ii grm. owing to the 
excess of transpiration over absorption. Later in the day, from 12.35 P- m - 
onwards, the rate of absorption was greater than the rate of transpiration, 
and the water-content of the plant increased ; but in spite of this the stomata 
continued to close. 
It appears from this result that a small decrease in the water-content of 
the leaf does not produce stomatal closure. The continued opening of the 
stomata may have been due to increasing illumination, or on the other hand 
the loss of water may actually have caused the stomata to open as in the 
case of the preliminary stomatal opening during wilting which was described 
by Darwin and Pertz ( 11 ) and by Laidlaw and Knight ( 16 ). Iljin ( 13 ) also 
found open stomata in wilted plants. 
Thus the evidence supports Lloyd’s contention that stomata do not 
closely regulate the water-content of the leaf, since there is no stomatal 
closure in response to incipient drying and consequently no stomatal inhibi- 
tion of transpiration. 
