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72
fo
1, 1920) the sun was shining and a light breeze was blowing.
These estimations are of course too few to admit of our obtaining
from them any certain idea of the CO, percentage in the upper
regions of the forest. But a priori it seems likely that the CO,
percentage falls as the distance from the ground increases, and
that at the tree-tops during intensive assimilation, in still weather,
it may be supposed to fall below the normal. The figures given
also support this assumption.
In more extensively wooded districts the carbon dioxide produced
from the ground must in its diffusion pass the tree-tops too, and
doubtless constitutes a not inconsiderable surplus to their need of
CO,. That only a part of the carbon dioxide of the ground remains
in the vegetation was shown above by a comparison of the carbon
dioxide produced and absorbed on equal surfaces in the unit of
time. It may also be understood from the circumstance that the
air 13—2 m. above the ground shows a relatively high percentage
of CO,. The CO, production of the ground ought not therefore
to be a matter of indifference for the growth and increase of the
trees. A closer investigation of the division of the CO, concentra-
tion in the different strata of the air in the forest ought to yield
important results for forestry.
In the open field also the CO, concentration in the stratum of
air nearest the ground is greater than higher up. Worrwv (For-
schungen aus dem Gebiet d. Agrikulturphysik, Vol. VIII, p. 412),
found in a clover-field 0.033% CO, 0.02 m. above the ground, and
0.025% 2 m. above the ground. The CO, concentration on the
ground rises after manuring with natural manure (BonNEMANN 1920,
pp. 48 ff) But since the wind sweeps over the field much more
easily than through the forest, the meadow-plants must on the
average lie under considerably lower CO, concentration than the
forest-plants, even apart from the fact that less CO, is produced
on the ground in the meadow. From the experiments of WOLLNY
and others it would seem to follow that the plants in the open
country even lie partly under abnormal low conditions in regard
to the percentage of CO,. This may lead to a real shortage of
CO,, more particularly in large tracts of country covered with
vegetation, and this is also proved by the fact that the CO, per-
centage over the sea is in the day-time somewhat grealer than over
the land.
One conclusion among others that may be drawn is that the air
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