

1905. | 7 On Vegetable Assimilation and Resprrution. 415 
In the experiments in“ Assim. and Resp. III,” it was demonstrated for 
. cherry-laurel that the assimilation-maxima at a given temperature were 
practically identical for all similarly treated leaves of the same age on the 
same evergreen bush at any one season of the year. In July and August, 
1904, when our new experiments were performed, the cherry-laurel bears 
new leaves just come to maturity and also leaves of the previous year. 
Experiment showed that the latter have by now quite low assimilation 
temperature-maxima, but that the newly matured leaves give the same values 
as we found in April, 1902, and April, 1903. This agreement for three 
separate years gives one considerable confidence in this material. 
Occasionally a leaf will show marked individuality and give aberfant 
values, but this is very rare; Experiment XII furnishes a cuse. 
Let us consider firstly some preliminary experiments with various natural 
variations of illumination. 
As the object of this work has been to determine completely the relations 
between assimilation and all intensities of natural illumination, and, as our 
previous work has shown that it would be fallacious simply to regard a 
succession of assimilation readings in a succession of different illuminations 
as being solely determined by the light, it therefore becomes essential to 
make inquiry about each assimilation-value obtained, and to determine 
(either experimentally or statistically) whether the assimilation is or is, not 
being limited by the temperature of the leaf to a smaller amount than 
the light would provide. In the early experiments this point is not examined 
experimentally, but is argued out by reference to the data on p. 413, and 
sometimes to data obtained in subsequent experiments. 
In the first four of these experiments on illumination, the actual leaf- 
temperature was not determined thermo-electrically, but has been subse- 
quently roughly estimated by adding to the temperature of the bath such © 
allowance as later exact experiments showed to be appropriate for each 
condition of illumination. 
Experiment I.—Cherry-laurel; leaf of current year set up in the leaf- 
chamber during the night in bath with moderate flow of water through it, 
and no artificial heating throughout the experiment. The bath at first 
_ vertical and superficially darkened with black cloth. From 4.15 to 5.15 aM., 
an estimation of the darkened leaf was taken, which shows an apparent 
minute absorption of COz This is probably somewhat in error, as a slight 
respiratory production of CO, would have been expected ; the chamber was, 
however, not perfectly dark. As soon as the rising sun shone on the bath— 
at 6 o’clock—the black cloth was removed, and the bath adjusted by means 
