2<S2 LIFE MOVEMENTfc IN PLANTS 



impulse reached the motile organ 200 seconds after the 

 initiation of the positive response. The stem was thin 

 only 2 mm. in diameter. The velocity of excitatory 

 impulse in a transverse direction is thus O'Ol mm. per 

 second : transverse transmission is, for obvious reasons., a 

 much slower process than longitudinal transmission of exci- 

 tation : in the Mimosa stem this is about 4 mm. per second. 



Unilateral electric stimi.ilation : Experiment 105. — In 

 order to show that the effects described above are not due 

 to any particular modt^ of stimulation but to stimuli in 

 general, I carried out an Jidditional experiment, the 

 stimulus employed being electrical. Two tine pin-electrodps 

 were pricked into the stem, opposite to the responding 

 leaf of Mimosa ; these electrodes were placed vertically 

 one above the other, 5 mm. apart. After a suitable 

 period, allowed for i-ecovery from mechanical irrita- 

 tion, feeble tetanising electric shock was passed through the 

 electrodes. The responsive effects at the distal side of the 

 stem is precisely similar to those induced under unila- 



Fi(i. lul. — Response of leaf of Jiimosa under transverse transmission of 

 Iwctric stimulns. (Compare this with fig. 100.) 



teral photic stimulation ; that is to say, the tirst effect way, 

 an erectile movement of the leaf, indicative of an induced 



