194 RESEARCHES ON IRRITABILITY OF PLANTS 



of 12 seconds ; the negative impulse then reached the 

 leaflet, giving rise to the reversed negative response (fig. 104). 

 The transmission period of the negative impulse is thus 

 14 seconds for a distance of 30 mm. The distance was next 

 reduced to half, or 15 mm., and on repeating the stimulus 



Fig. 104. — Effect of dimi- 

 nishing the distance of 

 application of stimulus. 

 The lower record shows 

 diphasic response in Bio- 

 phytum, positive followed 

 by negative. By applying 

 stimulus nearer, the posi- 

 tive is masked by the 

 predominant negative 

 (upper record) . Frequency 

 of oscillation once in a 

 second. 



Fig. 105. — Positive (3), diphasic 

 (2), and negative response 

 (1) of Mimosa brought 

 about by gradual diminu- 

 tion of distance of appli- 

 cation of stimulus. 



the positive impulse was found masked, the negative 

 occurring alone after an interval of 6'5 seconds. 



I will next describe another experiment carried out with 

 Mimosa. Stimulus was applied on the stem at a distance 

 sufficiently great to give only the positive response. This 

 is shown in the lowest record in fig. 105. The point of 

 application of stimulus was then brought somewhat nearer, 

 with the result that a diphasic response took place, positive 

 followed by negative — as depicted in the middle record. 

 And finally, on applying stimulus still nearer, the positive 

 was completely masked by the predominant negative. 



