108 PLANT PHYSIOLOGY 



a wedge, and force them off. H. von Mohl showed that this and 

 other such naive conceptions were untenable, and he tried to point 

 out the true state of things. His discovery of the scission layer was a 

 great advance. 



Now, for the first time, it was recognized that the loosening of 

 leaves is brought about by an organic process. But von Mohl con- 

 ceived the question in a one-sided, almost purely morphological way. 

 Ten years later, when plant physiology started its larger develop- 

 ment upon German soil, did they for the first time begin to search 

 experimentally for the causes of leaf-fall, and since that time the 

 question has not been allowed to rest, because we have sought to 

 come at a complete solution by means of combined anatomical, 

 physiological, and biological researches. 1 



How much and how long plant physiology suffered in Germany 

 under the dominion of one-sided anatomical study we are taught 

 by the Anatomie und Physiologic of Schacht, which was much valued 

 at this time (1856-59). This work is based almost entirely upon 

 morphology; experimental study was relegated quite to the back- 

 grdund; the specifically physiological element is not in evidence. 



Yet another remarkable point in the development of German 

 plant physiology demands explanation, because it shows that, as a 

 result of meaningless, one-sided handling, disciplines mutually neces- 

 sary, instead of helping, have hindered each other. I refer to the 

 conflict of Liebig with the German plant physiologists. 



The humus theory, upheld at the end of the eighteenth century 

 by Hassenfratz, was completely overthrown by Ingen-Housz. Yet it 

 was revived again among the German agriculturists and accepted 

 by the German plant physiologists. Their one-sided morphological 

 conception of the life of the plant and their neglect of the study of 

 their great forerunners explains this peculiar fact. As is well known, 

 Liebig laid the new humus theory to rest, as Ingen-Housz had the old. 

 He did it on the basis of the exact methods of chemistry with yet 

 greater certainty than Ingen-Housz, and also with better results. 

 This was the cause which led to a conflict between Liebig and the 

 German plant physiologists, lasting forty years, which was of no 

 use to science, and only showed that Liebig did not understand 

 morphology and that the plant physiologists did not conceive 

 aright the chemistry of the plant. In one thing both parties were 

 wrong. They did not understand how much each was necessary to 

 the other, if they would really further physiology. 



The first botanist who studied and mastered equally anatomy and 

 physiology, and attained that balance between them which is neces- 



1 Wiesner, Untcrsuchungcn tiber die herbstliche Entlaubung der Holzgewuchse, 

 Sitzungsberichtc der Wiener Akademie der Wissenschaftcn, bd. 64 (1871). Ueber 

 die neuesten biologischen den Laubfall betreffenden Studien, s. Berirhteder Deulschen 

 Botanischcn Gcscilsch. 1904. Ueber den Sommer-Laub fall, Ueber Treiblaubfall. 



