386 FRANK W. BANCROFT 



lower organisms, or according to the trial and error method of 

 Jennings. The second question constitutes another difference of 

 opinion in the views of these two camps but it is of minor impor- 

 tance in comparison with the question to be considered under 

 this heading. 



This, as' I conceive it, is the fundamental issue at stake, though 

 it is barely possible that I may be doing Jennings an injustice in 

 supposing that his conception of 'trial and error' excludes a direct 

 heliotropic orientation. Thus, for instance, he says in summing up 

 the heliotropism in infusoria ('04, p. 64), "It is not in accordance 



with the tropism theory above set forth The whole 



reaction is a strongly marked example of the type of behavior 

 which may be called the 'method of trial and error. ' " This seems 

 perfectly clear, but the trouble is that in such cases Jennings is 

 always combating the ' local action theory of tropisms' which it 

 seems to me has not been held by most of the authors to whom it 

 has been attributed by Jennings. 



A. The "local action tropism theory'^ 



Much as I dislike to digress for the correction of a misunder- 

 standing, nevertheless a rather detailed discussion of the 'local 

 action theory' is necessary, as silence on the subject has already 

 been interpreted (Jennings, '08, p. 701) as assent; and in the ab- 

 sence of contradiction this misunderstanding is liable to continue 

 to grow as it has, for instance, in the case of Mast ('11, pp. 41, 

 85). 



Jennings says in summing up his section" on the ' essential points 

 of the tropism theory' ('04, p. 94), ''We will here attempt to sum- 

 marize these observations so far as they bear upon the essential 

 points in the theory of tropisms. In particular we will ask, (1) 

 Is the observed behavior brought about by orientation in the way 

 the theory of tropisms demands? (2) Does the evidence show 

 that the action of a stimulus is directly upon the motor organs of 

 that part of the body on which the stimulus impinges?" It is 

 this latter statement, that the tropism theory supposes the stimu- 

 lus to act directly upon the motor organs that adherents of the 



