VARIOUS MOVEMENTS IN PLANTS 171 



characteristics of the nervous impulse in the animal were 

 shown to be present in the corresponding impulse in the 

 plant ; thus rise of temperature accelerated the velocity 

 in both, lowering of temperature causing a retardation or 

 arrest. Anaesthetics and poisons arrested the impulse in 

 an identical manner. 



The crucial test of a new theory is in its power of pre- 

 dicting phenomena hitherto unknown, and Bose's prediction 

 of certain unexpected characteristics of impulse in animal 

 nerve has recently been verified. Bose discovered that 

 the nervous impulse in plant is of a dual character, a 

 positive followed by a negative. The positive gives rise 

 to expansion and erectile movement of the motile leaf ; 

 the negative on the other hand gives rise to contraction 

 and down movement of the leaf. Certain investigations 

 now being carried out by Bose seem to indicate that the 

 nervous impulse in the animal may also exhibit a dual 

 character. Of still higher importance is the possibility 

 of control of nervous impulse, for which Bose obtained his 

 clue from investigations carried out with plants. He was 

 thus able to confer on the nerve two opposite ' molecular 

 dispositions ' at will. Under one disposition the nervous 

 impulse was greatly enhanced during transit, and under 

 the opposite disposition it was retarded or became arrested. 

 We shall, in a subsequent chapter, dwell on the high 

 significance of these results. 



