DEVELOPMENT OF PLANT PHYSIOLOGY 115 



Whatever we may think on the cause of this phenomenon, philoso- 

 phy has stepped so far to the foreground within the natural sciences 

 that, in discussing the relations of the sciences to the plant physi- 

 ology of that time, I cannot avoid examining how far philosophy is 

 in debt to our science. 



The question what philosophy is has been very variously an- 

 swered. If we regard it in the widest sense as the science of all being 

 and happening, and especially of the underlying principles, it is then 

 evident that it, or at least part of it, must form a proper constitu- 

 ent of the natural sciences. 



The desire to penetrate the ultimate causes of phenomena is 

 deeply rooted in mankind. This desire, as Whewell at one time so 

 truly remarked, is a curiosity to reach beyond the goal, to step be- 

 yond the bounds, which shut in the human spirit. Within these 

 bounds rule the experiences of knowledge. Human knowledge shuns 

 everything which is not made sure by experience. Thus the limit 

 is drawn within which philosophy may and can make itself of ser- 

 vice in the natural sciences. 



He who follows the development of the natural sciences with a 

 comprehensive view must come to the result that a sound philosophy, 

 based upon experience, has always existed in natural science. The 

 problems which many scientific workers have set themselves are indeed 

 of a simple kind, so that a philosophical penetration into the objects 

 dealt with may not have been sought for by them. But the masters, 

 the leaders, have ever been philosophers, so far as they controlled 

 their observations with logical power, bound together scattered obser- 

 vations with an intellectual insight held in check by criticism, and 

 tested by experience the theories which they formulated. Herein, 

 however, is indicated the limit up to which speculation is permissible 

 in natural science. Hypothesis may be used as a means, but is justi- 

 fied only so long as it stands in harmony with experience. 



Such philosophy has obtained since the rejuvenescence of the 

 natural sciences, wherefore this period has properly been called the 

 inductive; such philosophy will and must always obtain, because 

 this kind of philosophy is the living element of natural science. 



I do not have in mind that philosophy used by students of the 

 natural sciences, but seldom called so by them, when I speak of the 

 help which they have sought for in philosophy, but rather of that 

 of the specific philosophers, or, as I may say, of the speculative 

 philosophy, or, in brief, of "philosophy." 



Highly instructive for the relation of philosophy to the study of 

 natural science is the relation of Newton to the previous philosophers. 

 This has been shown by Brewster. 1 The vortex theory of Descartes 



1 Brewster, Sir Isaak Newtons Leben, Deutsche Uebersetzung, Leipzig, 1833, 

 p. 276 ff. 



