Stomata , Leaf Water-content , and Wilting of Plants. 37 7 
In no case was a decrease in water-content of more than 1 -6 per cent, 
found, and it is possible that as much as o -6 per cent of this was the original 
difference between the two companion leaves. The average decrease must 
be very small, and with the method used it is impossible to determine it 
with accuracy. The result was rather surprising, since the leaves showing 
this small decrease in water-content were definitely flaccid. To supplement 
these results a series of leaves were removed from the plant and allowed to 
wilt for ten, twenty, and thirty minutes respectively before weighing for water- 
content determinations. Observations were made of the appearance of the 
leaves at the time of weighing and determinations were carried out on 
companion leaves at the same time, as indicated in Table V. 
Table V. 
Water-content 
of turgid leaf. 
Duration 
of wilting 
period. 
Water-content 
at end of 
period. 
Decrease 
in water- 
content. 
84.7 
10 min. 
83-9 
0.8 
86.0 
20 „ 
85-4 
o-6 
84.7 
30 „ 
83-9 
c.8 
Appearance of leaf . 
Leaf distinctly flabby. 
Limp, lustre lost. 
Limp. 
These figures demonstrate that extreme flaccidity results from a 
decrease of approximately 1 per cent, in leaf water-content. In fact it is 
easier to detect the early stages of wilting by direct observation than by 
determination of decrease of water-content. It must be emphasized that 
the foregoing series of experiments does not actually demonstrate that the 
stomatal opening which occurs during wilting is brought about by a loss of 
1 per cent, of the water in any particular portion of the leaf — for example, 
the epidermal cells. The leaf has been treated as a whole in the water- 
content determinations, and it is conceivable that, although the mean decrease 
is only 1 per cent., the water concerned in wilting, i. e. that contained in 
the cell sap, may have decreased by a much larger amount. At the same 
time it is remarkable that a mean decrease of this magnitude should result 
in such a far-reaching effect as the production of the extreme flaccidity 
observed. 
Interpretation of the phenomenon in terms of single cells results in the 
rather surprising conclusion that the cell wall is only very slightly distended 
in the normal turgid state of the cell. The loss of small quantities of water 
from a cell with an elastic cell wall would simply result in a slight general 
contraction of the whole structure without any such loss of turgidity as is 
indicated by the collapse of the leaf. It may of course be possible to distend 
the cell walls of an already turgid plant by restricting transpiration whilst 
facilitating water absoption, but the foregoing experiments dealt with typical 
mesophytes in normal environment, and it is under these conditions that the 
conclusions are intended to apply. Since visible flaccidity is brought 
about by such small changes of water-content it is evident that the water 
