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64
this relatively high intensity the advantage of increased CO, tension
is very great.
The results obtained can therefore only be explained on the
assumption that the decisive factors for the assimilation influence
each other’s degree of activity. With light-intensities under ;4,—34 and
a carbon dioxide concentralion of 0.5; mg. per litre, both the light
and the carbon dioxide therefore work as »controlling factors».
It is worthy of note that the same result was obtained in the
case of all three of the plants examined with intensity ;44, which
seems to indicate that we have here to do with a state of affairs
that is of general application, at least for shade-plants. That the
phenomenon is of the greatest ecological importance follows from
the fact, demonstrated below, that the supply of CO, is usually
more abundant in the undergrowth of the forest than in the open
field. The shade-plants live their lives in great measure under
light-intensities below j,—., but with higher CO, concentrations
than 0.5; mg. per litre. The following figures show the increase in
assimilation with low and high light-intensity for two shade-plants.
Oxalis.
ES o. Assimilation 18°, 50 cm.2, |
Light-intensity Amount of CO, per |. | An 1 Pen |
ao 0.57 mg. 0.45 mg. N
» 2x0.57 » 0.9 |
3X0.57 >» 1.35 |
1 0.57 mg 2.3 mg |
1 .57 mg. 2.3 mg
| 2 X 0.5: 29 » }
3X 0.57 3.6 > i
Stellaria nemorum.
UM : ssimilation 18°, 5 3
Light-intensity Amount of CO, per 1. Suess te 50 em.?,
Ar 0.57 mg. 0.7 mg. |
2X 0.57 0.9 |
3 X 0.57 1o » |
1 0.57 mg. 1.5 mg |
2x05 » 29 |
|
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