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66
5. The natural CO, concentration.
The results given in the preceding section acquire their ecological
importance only when the natural CO, percentage of the air is
known. A very exlensive literature exists dealing with the com-
position of the air.
Numerous experiments have shown that the CO, concentration
over land and sea varies within quite narrow limits, with an average
value of about 0.03 volumes per cent, or about 0.55 mg. per litre,
calculated at 18° and 760 m/m (see lists in WorıLny, Forsch. d.
Agricullurphysik, Vol. VIII, p. 407, Lerrs and BLAKE 1900, BonNE-
MANN 1920, p. 45, REınau 1920, pp. 1 ff.). Fr. ScuULTZE (Versuchs-
stalionen, Vol. 14, 1871, p. 366) obtained as average value from 1600
analyses 0.029 vol. 4: Lerrs and BLAKE (1900) got the same value
from 46 analyses. An idea of the breadth of variation may be
oblained e. g. from C. WiLLIAMS’s 142 analyses made in Sheffield
(Berl. Ber., Vol. 30, 1897, p. 1451). He obtained as minimum value
0.0», and as maximum 0.051 vol. % Brown and EscowBk (Proc.
Royal Soc., 76 B, 1905, p. 118) obtained from 91 analyses, carried
out in the course of 4 years at Kew, a minimum of 2.43, and a
maximum of 3. vol. % CO,.
Some idea of the variation of the CO, percentage by the sea may
be formed from my 83 estimations carried out from June to Sep-
tember, 1920.
The variation of the CO, percentage from June to September 1920 at the
Ecological Station,
CO, in mg. per litre air
40 45 50 55 60 65 70 75 80
Pr URINE
| |
Numbers of variants) 4 | 1 9 22 27 We tds eke da
The cause of the varialions in the composilion of the sea-air on
Hallands Väderö is probably associated to some extent wilh the
winds. In general it has been found that in the day-lime land-
breezes conlain a little less CO, than sea breezes: at night the
opposile is the case. My figures point to a confirmation of this
theory, allhough the material is still too small to admit of more
definile conclusions. A comparison of the literature in LETTS and
BLAKE (1900, p. 182) shows a surplus value in the night-time of
2—14 % over the land. Other factors affecting the CO, percentage
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