364 Curtis: SOME OBSERVATIONS ON TRANSPIRATION 
or more probably quite nullify the value of the observations. As 
will be seen the measurements show an unmistakable curve char- 
acterized by minor fluctuations but demonstrating a grand curve 
with a maximum in the forenoon or near the middle of the day. 
In several instances I have noticed that transpiration was more 
active earlier in the day than was found in the first table. This 
may be due to the fact that the electric current was not turned on 
till 7 o’clock and the escape of the excess of intercellular vapor in 
the following hours overbalanced the normal transpiration under the 
feeble illumination. 1 regret that it was impossible to secure the 
curve for 24 hours under constant illumination. However, it will 
be seen that the curves for 12 hours bear a resemblance to the 
Irregular daily curve of growth determined by Sachs. The absorp” 
tion curves given by Vesque, also the curves of fluid tensions in the 
stem determined by Detmer and the periodicity of the exudation of 
fluids from cut stems, all show variations in keeping with the 
records set forth in Table II. It is interesting to note that these 
curves correspond in the main with those found in Table I, and 
show the same erratic character. Every plant appears to possess 
an individuality that becomes evident in these continued irregu- 
larities. In fact it has never been my experience to secure two 
measurements from the same plant that showed similar fluctua- 
tions, although special attention was given to placing them under 
the same conditions for two or more days between the tests. 
While there may not necessarily be a constant relation betwee? 
absorption, exudation and tension of fluids and the phenomena of 
growth, nevertheless, analogy and the general harmonizing of 
the ratios of these various rhythms with the curves of transpira- 
tion would seem to point unmistakably to the dependence of the 
latter process upon the vital activities of the plant. The marked 
irregularities in the rate are of special significance in this regard. 
As had been said they cannot be connected with any minor varia- 
tions of the light, temperature or humidity—at least this state- 
ment would apply to many of the experiments where the instru 
ments would show no appreciable fluctuations for hours at # 
time. Furthermore these results would naturally be expected 
where we consider Pfeffer’s work on the energy of the cell. 5° 
many factors enter that the secretion and excretion are constantly 
