186 Professor Jagadis Ch under Bose [May 20, 



accurate measureinents of time-intervals shorter than a hundredth 

 part of a second ; but skiggishness of our perception makes such an 

 attempt an impossil)ilitj. It is therefore absolutely necessary to 

 invent a special device by which the plant itself should be compelled 

 to write down its own latent period. In the case of the leg-muscle 

 of a frog, the latent period, according to Helmholtz, is about a 

 hundredth part of a second. This result is not without some error, 

 on account of the inertia of the recording lever, and the inferring of 

 time-relations from a neighbouring chronographic record. In my 

 Resonant Recorder these errors have been reduced to a minimum. 

 In the first place, the curve of response or phytogram is at the same 

 time a chronogram. Secondly, the weight of my plant recorder is 

 only a hundredth part of the usual muscle-recorder. The latent 

 period of the animal tissue undergoes appropriate variation with 

 chanaing: external conditions. With feeble stimulus it has a definite 



Fig. 11. — Record showing the Latent Period of Mimosa. This recorder 

 vibrates 200 times per second. The time-interval between successive dots is 

 here 0*005 sec. 



value ; this l)ecomes shortened under a stronger blow. Again, when 

 we are tired our perception-time becomes prolonged. Every one of 

 these results is equally applicable in the case of the plant. The 

 delicacy of the Resonant Recorder will be understood from the 

 response curve exhibiting the latent period of Mimosa (Fig. 11). 

 Here determination is carried to a thousandth part of a second, the 

 value being O'OTG sec, or eight times its value in an energetic frog ! 

 The reliability of this method can be gauged from successive records 

 under uniform conditions, when the results are found to be identical. 

 Another curious thing is that a stoutish plant will give its response 

 in a slow and lordly fashion, whereas a thin one attains the acme of 

 its excitement in an incredibly short time ! Perhaps some of us can 

 tell from our own experience whether similar differences obtain . 

 amongst human kind. The perception-time of the plant becomes 



