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85
in Nasturtium palustre, as has been said, at about 4; light. In Afri-
plex the point of equilibrium seems to be already reached al about
qo light (see table XII). In the sun-plant Sinapis alba, examined
by BovsEN-JENSEN (1918), the point of equilibrium seems to lie at
go light, in the apple-leaves examined by STÅLFELT (1920) at 4,
light. The sun-plants therefore scem quite generally to have their
light-minimum 2—4 times higher than the shade-plants (cp. p. 76),
which partly explains why they cannot bear deeper shade.
SUMMARY.
The object in view has been to ascerlain the intensity of assi-
milation in certain typical forest-plants, viz. Oxalis Acelosella, Stel-
laria nemorum, Melandrium rubrum, and Circea alpina, under diffe-
rent lights and supplies of CO,, and at the same time to examine
the conditions of light, the CO, conce tration, and the temperature
of the habitats, in order to arrive at an idea of the production of
organic substance under the natural conditions. In addition to the
forest-plants, a typical shore-plant, Nasturtium palustre, was also more
closely examined.
The estimations of the assimilalion were carried out by means
of a new apparatus constructed for ecological use. The principle
of this apparatus is that the assimilation-chamber also conslitutes
an absorption-vessel for the carbon dioxide, which is estimated over
a baryta solution with a wide surface. The same appara!us was
used for the estimation of the respiration and of the carbon dioxide
of the air. For purposes of comparison the usual method with an
air-current and absorption in a PETTENKOFER lube was also employed.
— In the estimations of the assimilation the following results were
obtained: —
1. With a variation of the light-intensity and with normal CO,
percentage in the air (0.57 mg. per litre), curves of the BLACKMAN
type were obtained for all the shade-plants. With lightup to 3o— 36
the assimilation seems to be more or less proportional to the in-
tensity of light. Above jy light no further rise took place.
For Nasturtium a curve of a more logarithmic pattern was ob-
tained.
2. With constant light the assimilation rises wilh the CO, supply
up to a certain height, which is delermined by the light intensity.
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