DIA-PHOTOTROPISM AND NEGATIVE PHOTOTROPISM 3:U 



pulvinus was 1-5 ijira., the distance which the excitatory 

 impulse has to traverse to reach the lower half would thus 

 be about 0-75 mm. The period for transverse transmission 



Fig. 120. — Record of effect of continuous application of light on upper half 

 of pulvinus of Mimosa leaf. Note erectile response (positive curvature) 

 followed by neutralisation and pronounced reversal into negative due to trans- 

 verse conduction of excitation. Up-movement shown bj' down curve, and vice 

 versa. 



of excitation under strong light was found to vary in 

 different cases from oO to 80 seconds. The velocity of 

 transmission of excitation in a transverse direction through 

 the pulvinus is about 0*011 mm. per second, which is 

 not very different from O'OIO mm. per second in the stem 

 (p. 282). 



Returning to the main experiment we find that : 



(1) As a result of unilateral action of light, there was 

 positive phototropic curvature which lasted for 

 50 seconds. 



