ill-luck constantly overlooks what is valuable in itself and
important in its results, Meyen generally picks out the best
things from the books before him; Treviranus timidly avoids
expressing any view decidedly and maintaining it; Meyen, amid
the multiplicity of the labours which we have already described,
finds no time to arrange his thoughts, is hasty in judgment
and often contradicts himself. But with all these defects, he
is still the champion of the new tendencies that were being
developed, while Treviranus lives entirely in the past, and
shows no trace of the actively creative spirit which was soon to
burst forth so mightily in every branch of natural science.
If we examine what both these writers have said on the subject of the nutrition of plants, we shall find that the difference in their general views in physiology as described above appears at once in their treatment of the work of suction in the roots, and of the means by which the sap ascends; here in Treviranus the vital force is everything; it makes the vessels of the wood conduct the juices from the roots into the leaves, with other antiquated notions of the kind; Meyen on the contrary adopts Dutrochet's position, and even rejects De Candolle's spongioles. Treviranus knows not what to make of respiration; Meyen explains it without hesitation as a function that answers to respiration in animals, and finds in it the main cause of the natural heat which Treviranus derives in the old mystical fashion from the vital force. In one point however they agree, namely, in a complete misconception of the connection between the decomposition of carbon dioxide in the leaves and the general nutrition of the plant. It is necessary to the understanding of the confusion of ideas which had crept at this time into the doctrine of nutrition, and to a right estimate of the services of Liebig and Boussingault on this point, that we should look a little more closely into the chemical part of the theory of nutrition in Treviranus and Meyen.
Treviranus in the introduction to his book repudiated the idea of a vital force separable from matter, but he was in fact
