44 RESEARCHES ON IRRITABILITY OF PLANTS 



was the duration of this particular record. The recovery 

 was completed after a further period of 20 minutes, that is 

 to say, the total period of recovery was an hour. The apex 

 time or period of contraction is shortened by the application 

 of a stronger stimulus, but the period of recovery then 

 becomes very much prolonged. The following tabular 

 statement will display the range of variation in the speed of 

 reaction of these sensitive plants : — 



Table showing Apex-times and Periods of Recovery in 

 Different Plants 



Arbitrary Distinction of Sensitive and Ordinary 



Plants 



The arbitrary distinction that is generally drawn between 

 the so-called sensitive and ordinary plants may briefly be 

 referred to here. In the case of Mimosa, it is generally 

 supposed that the lower half of the pulvinus is alone sensi- 

 tive ; this however is not an accurate statement. By local 

 application of stimulus it can be shown that the upper 

 half also undergoes a feeble contraction, causing an * up ' 

 movement of the leaf. 



The localised stimulus may be applied by means of the 

 electro-thermic stimulator. Application of stimulus of 

 moderate intensity on the upper half of the pulvinus will 

 be found to give rise to an erectile response. Another prac- 

 tical method of local application of stimulus is by means of 

 sunlight. A narrow beam may thus be thrown on the 

 upper half of the pulvinus; this will be found to give 

 rise to erectile or * up ' response. Two such responses are 



