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62
direct proportionality between the CO, supply and assimilation in
the cases given only holds good approximately, but that the method
of experiment does not permit of an estimation of the extent of
the deviation.
In other cases, however, the deviation from proportionality may
quite well be measured. My experiments with Oxalis and Stellaria
nemorum at about X light make this clear. Here the values for
the assimilation at abnormal CO, concentrations proved lower than
was to be expected.
6
Light |r
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Fig. 6. Diagram showing the influence of CO, supply on the CO, assimilation of
Stellaria nemorum at different intensities of light. For Melandrium, see table VIII.
The experiments with low light-intensities show a very interesting
deviation from BLACKMAN’s theory. As appears from the curves
for the influence of light (fig. 2, p. 55), in the shade-plants the
light at intensities under j;—4j; works as the limiting factor.
Only with intensities above ;,—;!; does the carbon dioxide appear
as limiting factor. Thus, according to BLACKMAN’S theory it ought
to be expected that with a light-intensily of e. g. 3, an increase
in the CO, percentage of the air over 0.57 mg. per litre would
not result in any rise in the assimilation. The experiments however
show that a rise actually does take place, wilh the same regularity
as with light-intensity } (see figs. 5, 6). In Stellaria nemorum and
Melandrium the maximum increase in the assimilation constituted
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