216 GROWTH HORMONES IN PLANTS 



then was replaced, traumatic or thigmatic stimulation of the tip 

 induced a response below the wound. In addition, such a 

 stimulus was transmitted when the coleoptile tip was placed 

 on the decapitated stump of another individual of the same species 

 or even of another species or another genus. The size of the 

 reaction, however, decreased more and more with the distance of 

 systematic relationship of the plants used. 



Nielsen (1924), using the Avena coleoptile, made a transverse 

 incision and, after the ensuing traumatic curvature had dis- 

 appeared, inserted a platinum plate in the wound. The tip was 

 stimulated then, by treating it on one side with silver nitrate, 

 above the incision. If it was stimulated on the side opposite the 

 transverse incision, a positive curvature developed in the basal 

 region; however, when the stimulus and incision were upon the 

 same side, no curvature resulted. This result was just the 

 opposite of that found for phototropic stimulus transmission in 

 relation to incisions. 



Transmission in Roots. — Fitting (1907) investigated the path 

 of stimulus conduction in wounded roots and found that it is not 

 hindered by a transverse incision made on the wounded side. 

 Similar experiments were carried out by Ivanovskaja (1929) 

 on the transmission of the traumatic stimulus in the root of 

 Lupinus alhus. Transverse incisions were made 2 mm. from the 

 tip, and mica plates were inserted. Then the root was stimu- 

 lated by sticking on one side of the tip a small piece of filter 

 paper, moistened with 0.03 to 0.05 M uranyl acetate solution 

 (U02(C2H302)2). It was fomid that the negative chemotropic 

 curvature was four times greater when the incision was placed 

 on the chemotropically stimulated side than when it was else- 

 where. This means that in these experiments the stimulus was 

 transmitted on the mistimulated side. Later (1930), it was 

 found that the chemotropic stimulus could be transmitted from a 

 root tip that was cut off and replaced on the stump. In addition, 

 it was shown that the stimulus was not intraspecific but that a 

 reaction resulted when a decapitated tip was placed on the root 

 stump of a plant from a different species, genus, or family. 



Transmission in Mimosa. — Much work has been done with the 

 transmission of stimuli in "sensitive plants" because of their 

 speciahzed means of response. It is beyond the scope of this 

 discussion to mention more than a few of these investigations. 



