37 2 Knight — Further Observations on the Transpiration , 
of the air during the various experiments gave a rough comparison of the 
evaporation rates and consequently of the rates of wilting, provided similar 
plants were used. Table II gives a list of experiments on Eupatorium 
adenophorum arranged according to the mean temperature of the air 
surrounding the plants during wilting. The table includes the percentage 
increase in size of stomata and in transpiration rate, and also the time 
which elapsed between the cessation of the absorption of water and the 
attainment of the maximum values of the two functions. 
TABLE ir. 
Results of experiments on Eupatorium adenophorum , showing the progress 
of transpiration rate and stomata! change during wilting at different 
temperatures. 
Mean 
'leriment 
temperature 
No. 
daring 
wilting. 
°C. 
39 
13-5 
4 i 
14.2 
3 * 
14.4 
37 
14-5 
36 
15.0 
42 
1 6-o 
43 
16. 1 
46 
16.4 
35 
17.4 
3 i 
18.4 
32 
18.8 
33 
19.0 
29 
— 
Percentage increase of: 
Stomatal 
aperture. 
Transpiration. 
- 
4 i 
25 
44 
— 
4 * 
574 
75 
153 
69 
27 
13 
16 
19 
— 
16 
44 
37 
— 
7 i 
— 
9 
— 
39 
— 
10 
Period elapsing before 
attainment of 
maximum [ minutes ]. 
Stomatal 
aperture. 
Transpiration . 
— 
64 
75 
75 
67 
49 
43 
37 
37 
30 
30 
5 1 
40 
— 
38 
31 
27 
26 
— 
21 
— 
18 
There is apparently no correlation between the temperature of the air 
in which wilting occurs (i. e. presumably the velocity of the wilting process) 
and the magnitude of the accompanying increase in transpiration 
rate. A similar remark applies to the increase in stomatal aperture. 
There is, however, a distinct relationship between the temperature during 
the experiment and the length of the interval between the commencement 
of wilting and the occurrence of the maximum transpiration rate ; this 
interval may be briefly termed the * preliminary acceleration period \ 
Table II shows that the length of this period varies approximately inversely 
as the temperature. Experiments 39, 43, and 46 are aberrant, but with the 
data available tw r o of these discrepancies can be accounted for. The relative 
humidity of the air in the greenhouse in which the experiments were carried 
out generally varied inversely with the temperature. In Experiment 39, 
however, the degree of saturation was unusually low for the temperature — 
70 per cent, instead of over 80 per cent. This would, of course, tend to 
increase the velocity of wilting. Conversely, in Expt. 43 the humidity was 
79 per cent, instead of about 70 per cent., which was more usual at 1 6° C., 
