434 RELATION OF PLANT PHYSIOLOGY TO OTHER SCIENCES. 



deal with a whole series of questions in osmotics from the standpoint 

 of pure physics. As a result, an insight was attained by which the 

 significance and explanation of numerous processes in plant life could 

 be arrived at. Moreover, the experiments of this plant physiologist 

 formed the foundation upon which was built the now famous Van't 

 Hoff's theory of osmotic pressure, which, according to this theory, 

 comes about in a way analogous to that of gas pressure. This is not 

 the first time that plant physiologists have taken up the question with 

 helpful results in the theory of osmosis. The genial and many sided 

 Dutrocbet, the discoverer of " exosmosis and endosmosis," was in the 

 front rank of plant physiologists. 



As with chemistry and physics, plant physiology stands also in this 

 relation of reciprocal exchange with meteorology and climatology. How 

 greatly plant life is affected by meteorological conditions and how the 

 distribution of vegetation is dependent upon climate is evident every- 

 where, and rich is the knowledge which plant physiologists have gained 

 by the application of the teachings of these two sciences. But in cer- 

 tain investigations relating to the life processes of plants these teach- 

 ings did not suffice, and so, on the part of plant physiologists, many 

 climatological and meteorological questions had to be taken in hand. 

 For example, one physiologist, in order to learn the mechanical effect 

 of rain, i. e., to find out the exact force of large rain drops on leaves, 

 determined the weight of the heaviest rain drops, the velocity of fall, 

 and the working force of falling rain. Likewise, contributions to a 

 more exact knowledge of the importance and significance of light to 

 plant life were made by plant physiologists. 



The connection between science and life has never been so conspicu- 

 ous as now at the turning of this century, and will doubtless become 

 yet more striking in the next century. Proud overbearance on the one 

 hand and a capacity for misunderstanding on the other have often and 

 for a long time maintained a sharp antagonism between science and 

 practical life, which rested with both sides on insufficiency of knowledge 

 and narrowness of view. Really great investigators always recognize 

 that, as Helmholtz opportunely expressed it, knowledge alone is not 

 the end of mankind upon the earth, but that knowledge should be 

 applied in the affairs of practical life. Only in this sense is knowledge 

 power, as Helmholtz thoughtfully added on the same occasion. 



The great botanical reformer, Schleiden, declared in the middle of 

 the century to his fellow-botanists, who absolutely disregarded the 

 application of botany in practical affairs: "All the industries which 

 make use of vegetable stuffs in manufacturing, etc., in doubtful cases 

 ask in vain of botany for information, although it is in a position to 

 direct and advise the industries, but it has no practical knowledge to 

 give ; knows least, often, the very plants which furnish the most 

 important stuffs, and borrows even from artisans themselves every- 



