220 EFFECTS ON TROPISTIC RESPONSE 



lation by the radium rays, are referred to in Chapter II. Koernicke's ' 

 experiments in this direction led to somewhat contradictory results, 

 and he concludes that there is no response to the beta and gamma 

 rays, but that, if the activity of the preparation is sufficiently strong, 

 plants may bend toward the phosphorescent light of the preparation. 

 He used Phycomyces nitens and Vicia sativa. 



I have tried very many experiments with a wide variety of spe- 

 cies, but always with negative or indifferent results, so far as con- 

 cerns the direct influence of the beta and gamma rays. Neither 

 roots nor shoots growing in air have ever shown the slightest ten- 

 dency to curve toward or from sealed glass tubes containing radium 

 of various activities. 



The tropistic behavior of plants with reference to the electric cur- 

 rent is a problem closely related to that of a possible radiotropism. It 

 was Elfving^ who, in 1882, first experimentally established the fact 

 that roots grown in water or in sawdust may bend toward the posi- 

 tive electrode, and he introduced the term " galvanotropic " to desig- 

 nate this property. Twenty years later. Plowman^ published a 

 paper dealing with the same question, and confirming the correct- 

 ness of Elfving's results. In 1904 he ^ proposed the term " electro- 

 tropism " as being more appropriate than galvanotropism. He found 

 that negative charges of electricity " stimulate" and positive charges 

 " paralyze" the embryonic protoplasm of the plants used, and there- 

 fore explained the electrotropic curvatures as due to the retarding 

 effect of the positive anions on one side of the root, and the acceler- 

 ating effect of the negative cations on the opposite side. This inter- 

 pretation is in harmony with results obtained by Matthews" with the 

 sciatic nerve of the frog. Matthews inferred that, "It is not the 

 charge, but its motion and sign, which ultimately determines its 

 action," and reached the conclusion that chemical stimulation, light 

 stimulation, and electrical stimulation are identical in nature. 



While nothing but failure followed all of my attempts to secure a 

 direct tropistic response to radium rays, it was thought that, if these 

 rays could be employed as ionizers of salts in solution, like the elec- 

 tric current in the experiments of Elfving and Matthews, tropistic 

 curvatures could be thus indirectly induced.* In essentials most of 



*The entire question of the effect of radium rays on salts in solution needs further 

 experimental investigation. In 1902 M. Curie' stated that the rays act on liquid 

 dielectrics as on air, rendering them conductors to a slight degree. Kohlrausch,^ how- 



