376 Knight . — Further Observations on the Transpiration , 
There is a great variation in the water-content of different leaves, even 
if the very young leaves at the tip of the shoot are excluded, but the 
difference between the two companion leaves from the same node is much 
smaller, amounting on the average to 0*3 per cent, with a maximum in 6 A 
and 6 B of o-6 per cent. Large differences in the water-content of different 
aged leaves were also found in the other species used, which included a 
Fuchsia species, an Abutilon , ivy-leaved Pelargonium, Morus nigra , and 
Pleroma macrantha. In view of the results obtained with companion 
leaves, trials were made with companion leaflets of pinnate leaves of a 
weeping ash and Juglans regia , and it was found that the figures obtained 
for these were in even closer agreement than those from companion leaves. 
Having obtained information with regard to the water-content of 
different leaves, the procedure was as follows: A record of stomatal aper- 
ture was obtained from a leaf under ordinary conditions, and at a convenient 
time the leaf was detached from the plant and allowed to wilt, the stomatal 
record being continued. When this leaf was detached its companion leaf 
was also detached and its water-content determined. When the stomata of 
the wilted leaf had ceased their preliminary opening movement and had 
begun to close, the stomatal record was stopped, and the leaf was removed 
from the leaf-chamber, weighed, and dried in the usual manner for water- 
content determination. The difference between the two values thus obtained 
represented the change of water-content of the leaf in passing from a con- 
dition of turgidity to the stage of wilting marked by the attainment of 
maximum preliminary stomatal opening. Account must of course be 
taken of the limits of accuracy imposed by the variation in water-content 
of companion leaves, which was demonstrated by Table III. The results of 
a series of these experiments are given in Table IV. 
Table IV. 
Showing change of water-content of a wilting leaf during the preliminary 
acceleration period. 
3® and 2, Fuchsia species. 6 , 7, 8, Eupatorium adenophorum . 
10, 11, Abutilon species. 
Water -content of leaf . 
Experiment No. 
Turgid. 
When stomata 
had ceased 
Difference. 
1 
88.9 
to open. 
88.7 
-0-2 
2 
88.1 
87.6 
87.4 
-0.5 
6 
87*2 
+ 0-2 
7 
87-2 
85.6 
-1-6 
8 
86.8 
86.7 
— O-I 
10 
78.4 
76.8 
— 1.6 
11 
79”9 
78.8 
— i*i 
