There is much in the details of Meyen's views on the
chemical processes in the nutrition of plants that is better than
what we find in Treviranus; it is a great point that he concluded from earlier experiments, that the salts which find their
way with the water into the roots are not merely 'stimulants'
but food-material, and, as was before said, he explained the
respiration of oxygen by plants correctly in accordance with de
Saussure's observation. But he too stumbled over the assimilation of carbon; he, like so many before and after him, was
confused by the simple fact, that gaseous matter takes part
both in the nutrition and the respiration of the plant; and
taking the processes in both cases for processes of respiration,
he considered the absorption of oxygen to be the only important and intelligible function, and the decomposition of
carbon dioxide in light to be a matter of indifference as
regards the internal economy of the plant. Instead of ascertaining by a simple calculation, whether the apparently small
quantity of carbon dioxide in the atmosphere was perhaps
sufficient to supply vegetation with carbon, he simply declared
it to be insufficient, and because plants will not flourish in
barren soil merely by being supplied with water containing
carbon dioxide, he gave up the importance of that gas altogether. He too found the humus-theory, which had been
constructed by the chemists, more convenient for his purpose, and like Treviranus derived the whole of the carbon in
plants from 'extract' of the soil, without any close attention
to the facts of the case; he refused to believe that the soil
is rendered not poorer but richer in humus by the plants that
grow on it. It is obvious then that the account given by
Treviranus and Meyen of the chemical processes that take
place in the nutrition of plants, though correct in some of
the details, could afford no true general view of the processes
of nutrition, because it entirely misconceived the cardinal
points in the whole theory, namely the source of the carbon,
and the co-operation of light and of the atmosphere; and
Page:History of botany (Sachs; Garnsey).djvu/543
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Chap. ii.]
of Plants. Treviranus and Meyen.
523
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