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17
determines the intensity of the assimilation. An increase in the
assimilation can therefore only take place by way of a raising of
the »limiting» or »controlling» minimum factor. However, as will
be seen in the following account of my researches, BLACKMAN’S
theory does not strictly apply when light is the minimum factor
opposed to the carbon dioxide. he shape of certain assimilation
curves also does not fully conform to Brackman’s idea (see also
O. WARBURG 1919).
My own researches are based on an ecological foundation. I have
set myself the task of examining the assimilation of various types
of plants under different external conditions realised in Nature, with
a view to thus ascertaining how these plants are adapted to their
habitats. My material was a number of typical forest-plants and
certain likewise typical shore-plants from Hallands Väderö, a small
island off the west coast of Sweden. The researches were carried
out at the Ecological Station on this island.
Two or three statements as to the influence of light on assimi-
lation in the case of sun-loving and shade-loving plants have already
appeared in the literature of the subject. Weis (1903) determined
by means of the Bonnıer-ManGın apparatus the intensity of assi-
milation in Oenothera and Polypodium. He found that in the sunlight
the assimilation of carbon dioxide is from 2 to 3 times more powerful
in Oenothera. In 4!, sunlight, on the other hand, Polypodium assimi-
lates more. LuBIMENKO’s (1905, 1907) and BovsEN-JENSEN’s researches
(1918) are more detailed. The latter determined the course of the
curves of light-assimilation in the sun-plants Sinapis alba, Senecio
silvaticus, Rumex Acetosella and Sambucus nigra, the shade-plant Oxalis
Acelosella, and the shade-loving varieties of Senecio and Sambucus.
’The result showed that the sun-plants in general have greater power
of utilising the intensive light than the shade-plants. My own re-
searches confirm this result.
Information as to the influence of the carbon dioxide on the
assimilation will also be found in the literature, and this will be
referred to below. But, on the other hand, no detailed examination
of the dependence of the plants upon the natural supply of carbon
dioxide or of the reciprocal influence of light and carbon dioxide
upon the form of the assimilation-curve has hitherto been attempted.
It is therefore upon these points that my own studies have been
directed.
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