Stomata , Leaf Water-content , and Witting of Plants. 381 
Table VI. 
Variation of leaf water-content at different times of the day. Eupatorimn 
adenophorum * Oct. 15* 1919. 
Change. 
8.30 a.m. 1 p.m. 
% 
80.4 
84.2 
84.8 
84-1 
83-4 
82.0 
83-5 
82.3 
83.0 
82.0 
82*5 
8i-6 
1.15 p.m. 5.15 p.m. 
79 * 1 
-i -3 
82.4 
82.5 
+ O.T 
83-3 
-0.9 
79.1 
79.8 
+ 0.7 
83^8 
— 1*0 
80.7 
81.7 
+ 1.0 
83.2 
-0.9 
82.6 
82.2 
-0.4 
82.7 
-0.7 
79-7 
79*9 
+ 0-2 
81.0 
— 1.0 
81.5 
81.6 
+ 0*1 
82*7 
-0.8 
81.8 
82.7 
+ 0-9 
8 r .9 
-0.4 
81.4 
82-4 
+ 1 -O 
83-3 
+ o *3 
83-4 
84.0 
+ 0-9 
81.7 
-o -3 
81. 1 
82.0 
+ 0.9 
83.8 
+ 1.3 
81.4 
81. 1 
^0.3 
81.7 
+ 0-1 
82.5 
82.9 
+ 0.4 
Mean : 
5 -°*5 
( ±o-i 
Mean : 
\ +° k 4 
( ±0.1 
Wafer loss from 
spherical cup 
atmomefer. 
Temperature 
Relative humidity 
i Max. 14-7° C. 12.30 p.m. 
( Min. 6-4° C. 8.30 a.m. 
Max. 86 % 5.0 p.m. 
Min. 57 % 11.30 a.m. 
Period. 
8.30 
9-3° 
3-5° 
5-30 
Grm. 
per hour. 
Twelve pairs of leaves were dealt with over each period, atid between 
8.30 a.m. and 1 p.m. the largest decrease in water-content was 1.3 per 
cent. During this same period one pair of leaves showed an increase of 1*3 
per cent., but it is of course probable that this was due to an initial difference 
in water-content between the two companion leaves. The average decrease 
of the twelve pairs was 0*5 per cent, with a probable error of o-i per cent, 
for this average. Three pairs showed an increase in water-content. 
The second portion of the experiment covered the afternoon hours 
when the atmospheric evaporating power, and doubtless also transpiration 
rate, were rapidly decreasing. Samples taken at 1.15 p.m. and 5*15 p.m. 
showed an average increase in water-content of 0-4 per cent., probable error 
o*i per cent. Two samples showed a decrease. 
Similar experiments have been carried out with a number of species 
and a resumS of the results is given in Table VII. 
Since it was evident that if the water-content of leaves decreased by 
more than about 1 per cent, flaccidity must occur, it was expected that no 
large diurnal changes would be found. Accordingly it was not surprising 
that in this series of determinations there is no indication of any diurnal 
change of leaf water-content of a magnitude corresponding to those found 
by Livingston and Brown, or even approaching those recorded by Clark. 
E e 
