520 Theory of the Nutrition [Book hi. 



vegetable physiologists at the close of the period before us, 

 Treviranus and Meyen, though they are not in accord with 

 one another in their general conception of the subject. It 

 may be said that all the prejudices and errors, built up on the 

 foundation of the hypothesis of a vital force during the first 

 thirty years of the 19th century, culminated in Treviranus ; 

 while others were already setting up the mechanical explana- 

 tion of the phenomena of vegetation as the one object to be 

 attained, Treviranus produced once more the whole machinery 

 of the obsolete doctrine of the vital force, and with such 

 effect, that his ' Physiologie der Gewachse ' was already obso- 

 lete when it appeared in 1835. The second volume of 

 Meyen's ' Neues System der Pflanzenphysiologie ' was a strik- 

 ing contrast to the work of Treviranus ; Meyen endeavours as 

 far as possible to trace back the phenomena of vegetation to 

 mechanical and chemical causes, though he does not often 

 succeed in bringing anything to light that is new or of lasting 

 service. He, like Treviranus, was deficient in sound training 

 in chemistry and physics ; they did not stand in this respect, 

 as Hales and Malpighi once did, at the highest point of know- 

 ledge of their time. At the same time there was a great 

 difference in the way in which each dealt with the writings of 

 his predecessors ; Treviranus, who had done good service in 

 former years in phytotomy, was not equal to the task which 

 he had now undertaken ; his physiological expositions are 

 marked by feebleness of thought and by an inability to survey 

 as from a higher ground the connection between the facts ; 

 he distrusts all that had been done during the previous thirty 

 years, and almost everywhere appeals to the publications of 

 the 1 8th century ; he lives indeed in the ideas of the past, 

 without gaining vigour from the forcible reasoning and fresh- 

 ness of thought of a Malpighi, a Mariotte, or a Hales. Meyen's 

 treatment of his subject is on the contrary fresh and vigorous ; 

 he does not disregard the old, but he holds chiefly to the 

 modern conquests of science; while Treviranus with singular 



