AUXIN TRANSPORT AND POLARITY 101 



as the auxin is present or applied in a concentration similar 

 to that normally obtaining in the plant, but that when the 

 applied concentration exceeds the normal by a factor of 100 

 times or so, the polarity disappears. An exactly similar 

 conclusion is reached in Chapter XI in regard to root forma- 

 tion, which is completely polar so long as auxin is applied 

 in concentrations of the same order of magnitude as those 

 in the plant, but which becomes non-polar when concen- 

 trations 100 to 1000 times the normal are used. No conclu- 

 sions can therefore be drawn from the indiscriminate applica- 

 tion of auxin paste of high concentrations, and no good 

 reason has yet been given for doubting the polarity of 

 normal auxin transport in the plant. 



E. Possible Mechanisms of Auxin Transport 



We have seen that auxin transport is not a process of 

 diffusion, both on account of its characteristics (especially 

 the velocity) and of its polarity. No satisfactory explanation 

 has yet been given for the transport. 



To account for the high velocity of transmission of the 

 phototropic stimulus, Brauner (1922) invoked the theory of 

 de Vries (1885) according to which the streaming protoplasm 

 carries with it organic materials, which are thus carried more 

 rapidly than they could diffuse. Went (1928) transferred 

 this view to the transport of auxin in the coleoptile. 

 Van der Weij (1932), however, opposed it because of the inde- 

 pendence of the transport velocity on temperature. Bottelier, 

 however (1934, 1935), has shown that between 17° and 35° C. 

 there is no appreciable change in the streaming velocity in 

 Avena at the age generally used. He has discovered a re- 

 markable parallelism between the effect of light on the 

 streaming velocity and the well-known light-growth reaction ; 

 both are proportional to the total energy and both show the 

 same variation with wave-length of the light. Further, the 

 amount of streaming protoplasm in the coleoptile shows a 

 daily and yearly variation which in many ways parallels 

 the, variation in sensitivity to auxin discussed in III C 8. 



