Leaf Water-content , and Transpiration Rate, 
229 
Fig. t. Graphs (based on results given in Table I) showing parallelism between stomatal 
aperture and relative transpiration. The graphs in this and the succeeding figure are plotted on different 
T 
base lines for the sake of clearness, s = stomatal aperture ; E = atmometer loss; - = relative 
E 
transpiration. 
The close agreement between the two is clearly shown by the maximum 
occurring in each between 12 noon and 12.30 p.m., and the small secondary 
maximum between 1.30 p.m. and 2 p.m. 
Experiment 11. A plant of Helianthus tuber osus was also used in this 
experiment, which was carried out in a manner exactly similar to that in 
Experiment 12. The results are shown in Table II and Fig. 2. 
In this case the two graphs appear to be quite independent of each 
other. Stomatal aperture reached a maximum at 11.45 a.m. and a second 
maximum at 1.55 p.m., but the relative transpiration graph shows only one 
maximum, and that between 2.50 p.m. and 3.20 p.m. 
From these experiments it is apparent that stomatal size and transpira- 
tion rate are not always in close agreement, and this result supports the 
conclusions reached by Lloyd using similar methods (19, p. 61). Darwin 
(9), however, claims to have shown a much closer agreement between the 
graphs of transpiration and stomata than has been found in the present work. 
In the above series of experiments, confirmation was sought of the 
observation of Livingston and others (see p. 221 above) that the maximum of 
relative transpiration occurs some hours previous to the time of the maximum 
of the evaporating power of the air. In Fig. 1 above it will be observed 
that the relative transpiration maximum fell between 12 noon and 12.30 p.m., 
whilst the evaporating power of the air was greatest between 2 and 3 p.m. 
R 
