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tion between pure physical or chemical processes and 
physiological phenomena. Most probably physiological 
phenomena are nothing but physical or chemical pheno- 
mena. This is sufliciently proved by the circumscription 
of the idea physiological process. It is used to denote, 
that, as yet we have not been able to reduce the process 
to a physical or chemical process, or rather, that it is 
not a simple physical or chemical phenomenon. When, 
besides with the more complicated, the physiological reac- 
tions of the living organisms we distinguish between 
actions caused by stimulation and processes with a dif- 
ferent result, the difference is not very marked. Truly 
speaking, it is hardly possible to give a definition of a 
stimulation-process. It seems to one that this is chiefly 
caused by the fact that many so-called stimulations are 
complicated reactions. With a chemotactical reaction we 
have to do with a change of an existing motion. As 
regards geotropism and phototropism we have to do with 
reactions of growing, that are altered under the influence 
of one-sided geotropical and phototropical stimuli. When 
we do not look upon these reactions, we receive a very 
complicated representation of them. Though we have no 
definition of a stimulation, yet we are convinced of the 
existence of it, when a connection is noticed between 
stimulus and reaction, which reminds us of the relation, 
stated by Weber's law, for stimulations from the phy- 
siology of animals and the experimental psychology. Also 
the inversion of the reaction by an increase of the stimulus 
would be characteristic of stimulation-processes. 
Ï think it better not to set too much value on both 
peculiarities, which can arise during stimulations. Weber's 
law concerning phenomena from plantphysiology, as far 
as it has been examined, goes into circumstances which 
do not differ too much. Besides this, the connection, 
stated by this law, needs not at all point to a physiological 
