194 



GROWTH HORMONES IN PLANTS 



Electrical potential and growth hormone transport in coleoptiles 



Electrotropism in roots 



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C 6 



T^ 



(PiR- 



Electrotropism 



Photo ■ and 

 electrotropism 



Mil 



Gravity 



Geo- and 

 electrotropism 



H 



i i i i 

 Gravity 



Fig. 60. — Electrical potential in relation to growth curvatures. In accordance 

 with its acid character, the active radical of the growth-hormone molecule 

 bears a negative charge; hence it should be moved toward the positive electrode 

 in an electrical circuit. Accumulated hormones in the relatively electropositive 

 tissues should regulate growth in agreement with the theory of growth-hormone 

 activity. Density of stippling indicates the presence and relative concentration 

 of the growth hormone. The diagrams show the setup and the resulting growth 

 response in each experiment. 



A, effect of an electrical field upon growth curvature. Upright coleoptiles 

 immersed in conductivity water bend toward the positive electrode in a circuit. 

 This may be explained on the assumption that the coleoptile with its cuticle 



