DEVELOPMENT OF PLANT PHYSIOLOGY 123 



chemistry, physics, meteorology, and climatology, and upon other 

 studies far distantly removed, according to earlier conceptions; and 

 that it will do this with still more advantage in the future. Plant 

 physiology is often in need of things, e. g., on the part of physics and 

 meteorology, which these sciences do not have to give her, so that 

 the plant physiologists are compelled to work independently in these 

 apparently strange fields. I may recall Pfeffer's important discoveries 

 in osmosis, which, as is well known, have been of great importance 

 in the theory of osmotic action. 



In order to learn the actual, but apparently highly overestimated 

 mechanical effect of rain upon plants, a close student of this question 

 had need of data which were not to be found in the meteorological lit- 

 erature, and himself determined the weight of the heaviest raindrop, 

 its rate of fall, and its kinetic energy. 1 From this study both plant 

 physiology and meteorology profited. The same plant physiologist, 

 incidentally to his studies of the use of light by plants, contributed 

 to the science of climatology by his thorough observations of photo- 

 chemical climate. 2 



These are random examples merely, but nevertheless indicate 

 that plant physiology is in condition to render service to the so- 

 called exact sciences. 



If I should speak a word for the later advantage to physics through 

 plant physiology, this might seem to be an oratio pro domo. For this 

 reason I refer to the remarks of a celebrated physicist. Ernst Mach 

 says in one of his best known works, "Not only may physics help 

 and clarify biology (in the widest sense as the doctrine of life), but 

 biology may stand in this relation to physics. . . . Physics will 

 accomplish yet more for biology, after it has grown by means of the 

 latter." 3 



I hasten to a close. I have not intended to present new facts, 

 but rather to use well-known ones in order to support my leading 

 thought to which I gave voice at the outset. 



I have tried to present to you a picture in which the development 

 of plant physiology under the influences of the other sciences is por- 

 trayed; but in reviewing it I feel that it is very incomplete. 



The disproportion between the extent of my duty and the time 

 at my disposal will explain in part the failure to realize my aim. 

 Still more, however, is this due to the difficulty of my subject, for 

 one must master all the sciences which stand in relation to plant 

 physiology in order to give an effective account of its development. 

 On account of the specialization to which we are all committed, 



1 Wiesner, Beitrage zur Kenntnis des tropischcn Regens, Sitzungsber. d. Wiener. 

 Akad. d. Wissensch., 1895. 



2 Wiesner, Beitriige zur Kenntnis des photochemischen Klimas, Denkschriften d. 

 Wiener. Akad. d. Wissenschaftcn, 1896 u. 1898. 



3 E. Mach, Analyse der Empfindungcn, Jena, 1902, p. 74. 



