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86
In Nasturtium and Viola tricolor at + light and in Oxalis and Me-
landrium at 3, light an approximate direct proportionality was ob-
tained between the CO, concentralion and the intensily of assi-
milation. In olher cases the assimilation rose more slowly than the
CO, concentralion.
3. An increase of the CO, absorption with abnormally high CO,
concentration in the air was observed even with small quantilies
of light (4,). From this fact it may be concluded that the light
and the carbon dioxide mutually affect each other’s influence as a
controlling factor. —
The examination of the natural conditions gave the following
results: —
4. The CO, production of the ground during the period of ve-
getation atlains considerable values. It is least for sandy soil, great-
est in Ihe mould of beech-woods. Very abundant CO, production
goes on in rotting beds of seaweed.
5. In the forest, on account of the CO, production of the ground,
the air is rich in carbon dioxide, especially nearest the ground,
where herbaceous plants live. The CO, percentage may here rise
to more than twice the normal. This increased supply of CO, is
an important condilion for the exislence of the shade-flora.
6. The supply of light in the forest varies extremely, owing to
the passage of the sunlight through the tree-tops. Patches of direct
sunlight fall from time to time upon the ground, and this fact is
of importance for the assimilation of the forest-plants.
7. The conditions of temperature prevailing in the forest, as
well as the moisture and the protection from wind. are favourable
to an anatomical leafstructure such as allows of the utilisation of
the light to the fullest possible extent.
8. The intensity of respir.ıtion is lower in the shade-plants than
in Nasturtium and other sun-plants. An equilibrium between re-
spiralion and assimilation is reached in the case of the shade-plants
at ;45—;40 light, with. normal air. In order that the daily assi-
milation may compensate the respiration of the night-time there is
required at 18° an average illumination of j; light. In order that
the growth of the vegelation may be maintained there is further
required, in the case of Oxalis, a minimum daily illumination of for
example i light for somewhat more than 1 hour.
9. Among the shade-plants Oxalis has the greatest maximum
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