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the light-intensities offered in Nature for our disposal, but, in com-
mon with all light-measurements given in the literature, they are
quite insufficient to be made the basis of a calculation of the
daily process of assimilalion in the forest-plants. The only possi
bility of obtaining information as to the variations in the condi-
tions of light in the forest is by a continuous registering, and the
lack of suitable apparatus has hitherto rendered this impossible
to carry out.
If the curves for the shade-plants are compared with one another,
it will be seen that the maximum assimilation varies. The con-
ditions are most favourable for Oxalis. This circumstance is natu-
rally of ecological importance, since it gives a different degree of
productive power under favourable conditions. The rise of the
curves in their left-hand sections also probably indicates variations
which point to specifically different powers of assimilation, due
possibly to different chlorophyll percentages or to different inten-
silies in the protoplasm factor. The experiments however are too
few in number to give a sufficiently exact determination of the
steepness of the curve in the strong individual variation.
4. The influence of the carbon dioxide concentration on the assimilation.
The influence of the CO, concentration upon the assimilation
has already been examined by GoprEwsk: (1874). The PFEFFER
apparatus used by him (PrErrEn 1874) certainly does not give any
great degree of accuracy. GODLEWSKI also used very high CO,
concentrations (1.2 4/1—42 4). He found that the assimilation rises
with an increase of the CO, concentration up to 5—10 7, and that
the rise becomes more pronounced the stronger the light is.
In view of Brown’s experiments (1902) and of my own as
described below, it seems as though it may be doubted whether
the rise in the assimilation really runs up to such high CO, con-
centrations. For the same reason it seems to me that a number
of KREUSLER’s values (1885) ought to be revised. KREUSLER however
employed a much better method than GODpLEWSKI, namely an air-
current with a comparatively low CO, concentration and gravi-
metric estimation of CO,. An average of the values obtained by
him for different plants gives a strikingly low and extended curve.
! For earlier, incomplete observations see Czarrk (1913, p. 527).
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