182 PHYTOHORMONES 



Their figures give no evidence that the ethylene produces 

 any increase in the total growth rate. It is most probable, 

 therefore, that the effect of the ethylene is to influence the 

 distribution of auxin in the petiole. 



We have seen above that gravity may do the same thing, 

 i.e. may cause unequal distribution of auxin. In a later 

 paper (1935), Crocker, Hitchcock, and Zimmerman have 

 argued that since application of auxin to the petiole can 

 also produce unequal growth, the action of ethylene is the 

 same as that of auxin. However, by the same argument, 

 the action of gravity should be the same as that of auxin, 

 i.e. gravity should be a growth hormone! This shows a 

 confusion between the primary factor (auxin) and the forces 

 which modify it, much as though the action of gasoline on 

 an automobile were to be compared with the changing of 

 the gears. Another unjustifiable comparison between ethyl- 

 ene and auxin is referred to in XI C. 



