116 PLANT PHYSIOLOGY 



was a real hindrance to the acceptance of Newton's theory of the 

 motions of the heavenly bodies. And concerning the assertion that 

 Newton depended upon Bacon, Brewster has shown conclusively 

 that Newton searched out the truth by observation and b}' experi- 

 ment in part worked out by himself and partly borrowed from 

 Copernicus and Galileo. 



But, in order to speak of the influences of philosophy on botany, 

 must we not point out Schleiden, who, it may be presumed, placed 

 this science upon a new basis? The methodological basis proposed by 

 him, which may be referred back to Kant, had the value of quite 

 setting aside the harmful academic philosophy of Schelling, which 

 caused not a little confusion among the mediocre botanists of that 

 time, and of adhering to exact observation and to the logical pre- 

 sentation of the facts. But the advance of our science by no means 

 took its origin from his philosophical teachings; this was effected 

 by students such as Hugo von Mohl and others. Schleiden's schemati- 

 zation of the cell was a fruitful idea, and his activity, in the sense of 

 Robert Brown in the field of ontogenetic development, brought a rich 

 return. But all this had nothing to do with the Fries-Appelt philoso- 

 phy, often cited by him, and with his continual reference to Bacon. 

 His criticism, however, often overshot the mark in matters of plant 

 physiology, and has hindered rather than helped on the develop- 

 ment of our science. The greater part of Saussure's experiments he 

 cast aside as "completely useless;" the fact that green plants in an 

 inclosed space can, in spite of gas exchange, keep the surrounding 

 air in a condition in which it remains apparently unchanged qualita- 

 tively and quantitatively, was regarded as an impossibility, and in 

 spite of Ingen-Housz and Saussure, it was boldly asserted that Bous- 

 singault first proved that green plants absorb carbon dioxid in 

 sunlight. Fechner's views in regard to the irritability of plants, 

 with \vhich all physiologists to-day agree, were not only opposed by 

 Schleiden from the philosophical standpoint, but he even scouted 

 them with derision. 



The whole literature shows how little use "philosophy" has been 

 to plant physiology. I will touch upon this with only one example, 

 which, however, will show also that students of science themselves 

 enter into abstract thought so far as it is advantageous to them in 

 the solution of their problems. Schopenhauer, in his work, Zur Phi- 

 losophic und Wissenschaft der Natur (1851), broke a lance for the 

 doctrine of vital force. His arguments against the purely mechanical 

 conception of life are completely justified; but it was these same 

 arguments which were advanced ten years ago by Johannes Miiller. 

 So far as Schopenhauer and Miiller are in accord with one an- 

 other on this point, the student of science can follow the philo- 

 sopher. But when he encroaches on the field of metaphysics, and 



