of nutrition, the first thing required was not the discovery of
new facts so much as the forming a correct appreciation of the
discoveries of Ingen-Houss, Senebier, and de Saussure, and
clearing away the misconceptions that had gathered round
them. The chief modern representatives of vegetable physiology, De Candolle, Treviranus, and Meyen, had increased the
difficulty of the task by neglecting to keep the several questions
of their science, the chemical especially and the mechanical,
sufficiently distinct from one another. The question, what are
the materials which as a rule compose the food of plants,
though one of the first and most immediate importance, had
been very imperfectly investigated, while attention had been
diverted to a confused mass of comparatively unimportant
matters, and the solution of that question had been rendered
impossible for the time by the humus-theory, an invention of
chemists and agriculturists, which Treviranus and others had
fitted so readily into the doctrine of a vital force. To Liebig
belongs the merit of removing these difficulties and all the
superfluous matter which had gradually gathered round the
subject, and of setting forth distinctly the points which had to
be considered; this was all that was required to ensure a satisfactory solution of the problem, for former observations had
supplied an abundance of empirical material. But some points
of minuter detail were brought out in the course of his
investigations which required new and comprehensive experiments, and for these a most capable and successful observer was found between 1840 and 1850 in the person of Boussingault.
But before we go on to give a fuller account of the work of Liebig and Boussingault, we may mention a circumstance which serves to indicate the character of the revolution in scientific opinion before and after 1840. An anonymous 'Friend of science' had put a prize at the disposal of the Academy of Gottingen for an answer to the questions, 'whether the inorganic elements, which are found in the ashes of plants. are found in the plants themselves, in cases where they are not
