ORGANIC MOVEMENTS 13 



this case. Whenever parts of a plant change the sense of 

 a tropisrn, according to their age or state of fertility, we find 

 something very similar. Here already the concept of the 

 " whole " with regard to functioning in its relation to out- 

 side factors presents itself, though perhaps not in a manner 

 sufficient to refute the " machine theory " of life. 1 



The last step of complication is reached if two or more 

 stimuli are in competition with one another. This case is 

 best shown by the behaviour of roots in the ground ; 

 gravity, moisture, heat, chemicals are the principal stimuli 

 concerned here. The effect is not a simple sum or resultant, 

 but a sort of unity of a very peculiar kind : each single 

 component may change the organism's sense of irritability, 

 or " Stimmung," towards any other component. A certain 

 sort of innate direction relative to the axis may be among 

 the components that influence the behaviour of a certain 

 organ (" autotropism "). It would at least be difficult to 

 apply the machine theory of life in these cases. 



So much on tropisms. 



Are the directive movements in freely moving Protista 

 or animals, called " taxis," explainable in the same way as 

 tropisms ? 



" Taxis " 



It is clear that the direction and the movement are two 

 different things. It is the direction only that is considered 

 here, and so we may better say : " taxis ' signifies the 

 specific orientation of a specific axis of the organism with 

 regard to the direction of any directed agent of the medium. 



1 A very strange case belonging here is discussed by France (Zeitschr. /. d. 

 Ausbau d. JEntwickelungslehre, i. 4, 1907). 



