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84
favoured both in regard to light and to carbon dioxide. Fig. 9 gives
an idea of the vegetation of the damp seaweed-beds.
The intensity of respiration is somewhat greater in Nasturlium
than in the forest-plants examined’. In the latter it amounted to
about 0.3 mg., in Nasturtium it is 0.4; mg. per 50 cm.?, 18°, and 1 hour
(average from 4 estimations) This value seems to be somewhat
lower than for olher sun-plants (Helianthus 0.7 mg., according to
BLACKMAN; cp. BovsEN-JENSEN 1918, p. 242).
In other shore-plants I have found much higher respiration-
values. Thus Aster Tripolium in the height of summer at about
28° C. breathes out 1.5 mg. CO, per 50 cm.? per hour. The intensily
of the respiralion depends upon the conditions of nourishment, and
my relatively low values for Nasturlium may perhaps be due to
the fact that the experiment was carried out at the beginning of
October, upon plants which had stood under less than normal light.
On sunny days the shore-plants live under light-intensities which
during the different hours of the day amount to the following values
(taken June 25—27, 1920):
3a. m. 4.4, m. 05.8. Im. 27:8. Imi OCA mA Deere
Wipe mies p: mi). /’ puo p nm t
1 1 1 1
50 10 B 3
Since respiration and assimilation in Nasturtium counterbalance
each other at about „, light (see fig. 3), pure losses by respiration
only come into question for a shorter portion of the night. No
completely reliable calculation of the extent of the daily production
of carbo-hydrates can be arrived at in regard to the seaweed ve-
gelation from the above figures. For the CO, concentration actually
affecting the leaf is very dilficult to estimate, and so also is the
temperature of the leaf. j
An equilibrium between respiration and assimilation is reached
! Several earlier investigators have proved that the shade-plants have lower in-
tensities of respiration than the sun-plants (see e. g. LAMARTIERE 1892, AD. MEYER
1892, HESSELMAN 1904, p. 400).
* These values can only be regarded as approximate. A similar series for |
Denmark has been given by BoysEN-JENSEN (1918, p. 234). As I have not fixed |
my unit of light in any of the usual scales, my light-values are not exactly com-
parable with those of any other investigator. However, the differences in the in-
tensity of the maximum light of heaven become great only if two places lie on
very different degrees of latitude or at different heights above sea-level.
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