122 PLANT PHYSIOLOGY 



for entropy, 1 and on the other side, the attempt has been made 

 to show, on the grounds of observation, what proportion of the 

 energy of the sun which is used on the earth by green plants is 

 rendered available for the life of organisms. I here come to the 

 calculation of Pfaundler and to the beautiful and important re- 

 searches carried on by Brown and Escombe to determine the 

 "economic coefficient," which have shown approximately how much 

 of the sun's energy is fixed by the transpiration of green plants in 

 the light, and by photosynthesis. It w r as found that in sunlight far 

 more energy is employed for the purpose of transpiration than for 

 that of photosynthesis, and that, in diffuse light, relatively more 

 energy, in comparison with transpiration, is consumed in photo- 

 synthesis than in sunlight. Since we in recent times recognize only 

 green plants as autotrophic, the opinion entirely problematical, to 

 be sure may well arise that life upon the earth must have begun 

 with green organisms. Now, however, as you know, it has been 

 shown by Hueppe and Winogradski that certain bacteria also fix 

 carbon dioxid, and are in every way to be regarded as autotrophic. 

 Chlorophyll is, then, not absolutely necessary to photosynthesis; 

 but rather has this become to us, according to our present under- 

 standing, in the course of the development of the plant world, a 

 wonderful, purposeful means of building up organic substance 

 under the influence of light. 



And yet many more details may thus be advanced, to show that 

 even one and the same problem may be brought to its solution by 

 the most different branches of science. 



I have, to be sure, only in the most cursory manner tried to show 

 how plant physiology has arisen under the influence of the other 

 branches of natural science, and, finally becoming a part of botany, 

 was advanced by morphology. 



How physiology has come into relation with the other branches of 

 science, especially the mental sciences, and has affected practical 

 life, has already been dwelt upon by me. 



In order to complete the picture of the interaction of the special 

 sciences, I would, at the close, draw attention to the fact that, young 

 as plant physiology is, it has been of help to pure science far beyond 

 the bounds of botany. 



I may mention the advance which plant geography, at first espe- 

 cially a statistical account of the plant world, has made since it was 

 organized upon physiological and ecological bases by Schimper, 

 Warming, and others. It is no paradox when I say that plant physi- 

 ology has reacted advantageously upon the further development of 



1 Boltzmann. Drr zu-eite Hauptsatz dcr mechanischcn Warmrthrnrie. Vortrag 

 Wiener. Akad. d. Wissrnfich., Almanack, 1886, p. 246. See also L. Pfaundler, Die 

 Wcltwirtschaft iin Lichtc der Physik, Deutsche Revue, 1902. 



