CHAP, ii.] of Plants. Liebig. 525 



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 physio- 

 logy, 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 satis- 

 factory 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 experi- 

 ments, 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 



