388 FRANK W. BANCROFT 



tropism theory' but on numerous occasions shows that the 

 motor organs are not acted on directly by the stimulating agent. 

 Thus on page 3 of the Comparative Physiology of the Brain from 

 which work the passage quoted by Jennings is taken, Loeb says, 

 ''The flight of the moth into the flame is a typical reflex process. 

 The light stimulates the peripheral sense organs, the stimulus 

 passes to the central nervous system, and from there to the 

 muscles of the wings and the moth is caused to fly into the flame. 

 This reflex process agrees in every point with the heliotropic 

 effect of light on plant organs. Since plants possess no nerves, 

 this identity of animal with plant heliotropism can offer but one 

 inference — these heliotropic effects must depend upon conditions 

 which are common to both animals and plants." This quotation 

 strikes the keynote of Loeb's attitude towards the tropisms. 

 Since he believes the tropisms are fundamentally similar in ani- 

 mals and plants he has been careful to speak of the tropisms in 

 general terms that might apply to either plants or animals. Jen- 

 nings seems to have consistently misunderstood these general 

 statements, and to have thought that they referred to only one 

 of the things that were included in them. 



With regard to Torrey, Jennings says ('08, p. 701) that he 

 'expressly defends the local action theory.' In his paper, 

 however, Torrey never mentions the local action theory by name, 

 and as I understand his paper the 'tropism hypothesis' that 

 Torrey is writing about is the usual theory of tropisms and not 

 the local action theory. I repeatedly discussed the question with 

 Dr. Torrey both before and after his paper was published and 

 know that he never believed in the local action theory. 



In conclusion I would like to add that I am not a believer in the 

 'local action tropism theory.' I would even go farther than 



stimulation of the muscles. I have looked over a number of the other papers to 

 which Jennings refers ('OG, p. 269) as advocating the local action tropism theory; 

 and among the papers examined I found only one which Jennings has not misunder- 

 stood in a similar way. The single exception is the paper by Holt and Lee who do 

 speak of the stimulation of the cilia by light. Thus, on the page referred to by 

 Jennings, Loeb ('00, p. 186) says "The chemical effects of the diffusing molecules on 

 certain elements of the skin influence the tension of the muscles." Here again 

 Jennings takes "certain elements of the skin" to mean muscles, etc. 



