184 



GROWTH HORMONES IN PLANTS 



the positive pole (Fig. 56). Both the coleoptile of Avena and the 

 root of Vicia were found to be positively charged on the lower side 

 when placed in a horizontal position (Fig. 57). At about the 

 same time, Hartmann (1932) obtained somewhat different results. 

 In experiments with 3,000 volts per centimeter, Avena coleoptiles 

 showed a weak bending toward the negative plate at 

 first and later exhibited curvatures toward the positive pole. 

 These curvatures were always very weak. Amlong (1933) since 

 has studied the electrotropic curvature of Helianthus seedlings 



according to the method of 

 Letellier, using a field of 1,000 

 volts per centimeter applied to 

 seedlings growing in a moist 

 chamber. The seedlings curved 

 away from the negatively 

 charged plate. 



Koch (1934) found that when 

 an electric current is applied 

 through upright coleoptiles 

 placed in conductivity water, 

 the coleoptiles do not conduct 

 the current; hence, within the 

 coleoptile a negative pole is 

 induced on one side, and the 

 coleoptile curves toward it (Fig. 

 60). When an electric current 



coleoptile toward the positive pole in -^vas applied tO rOOts of Pisum 

 an electric field. (From Brauner and , i i • i ^^ • j 



Biinning, 1930.) placed horizontally m conduc- 



tivity water, it was found that 

 they conducted the current and curved to the positive pole, away 

 from the force of gravity (Fig. 60). 



A good qualitative agreement has been found between the 

 course of geotropic and electrotropic curvatures, although the 

 former curvature is significantly stronger than the latter. It may 

 be conjectured that the geoelectric phenomenon is probably 

 essential but not the only necessary factor for the displacement of 

 growth substance. It should be remembered that although 

 growth substance may be present, its displacement does not 

 always occur under conditions of unilateral stimulation by light 

 or gravity. 



Avena 



