LECTURE VIII 



FURTHER FACTS CONCERNING TROPISMS AND RELATED 

 PHENOMENA 



I. General Theory of Tropisms * 



In the preceding lecture and in my former writings I had given a 

 theory of tropisms which may be considered as an appUcation of Fara- 

 day's conception of lines of force. We may conceive space as being 

 traversed by various kinds of lines of force, some of which are present 

 permanently, and in the same direction, e.g. lines of gravitation ; while 

 others may be present or absent, and may vary their direction, e.g. 

 light rays, or electrical lines of force, etc. The bodies of living organ- 

 isms possess as a rule a symmetrical structure, not only morphologically 

 but also chemically, or dynamically. By this I mean that symmetrical 

 points at the surface of the body of ah organism possess practically 

 the same chemical substances qualitatively as well as quantitatively, 

 and hence the velocity and kind of chemical reactions must be the same 

 for such symimetrical points. Asymmetrical points of the organism, 

 however, possess a different chemical structure, and hence the velocity 

 and kind of reaction does not need to be, and probably generally is 

 not, the same. 



It is presumed, and is in all probability true, that those forms of 

 energy which influence orientation or the direction of the motion of 

 an organism, do so because they alter the velocity or the character 

 of the reaction. 



On account of the symmetrical structure the organisms are oriented 

 automatically in any field of force which affects their chemical reactions 

 neither too little nor too much, in such a way, that symmetrical points 

 of the surface of the body are struck by the current curves at the same 

 angle. In this case each element of the surface receives the same num- 

 ber of current curves. 



The way in which this automatic orientation of the organism is 

 brought about has already been mentioned in a preceding lecture. If 



* Cf. Loeb, Pfluger's Archiv, Vol. 64, p. 439, 1897. 

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