DETERMINATION OF THE LATENT PERIOD 115 



All this takes place during the continuance of one pressure 

 of the handle. During the descent of the plate, stimulation 

 due to instantaneous break-shock takes place at the definite 

 moment corresponding to the stimulation mark. 



Electric connections are appropriately made with the 

 plant by means of threads moistened in dilute saline 

 solution. One electrode of the secondary coil is thus 

 connected with the stem of the specimen : the moistened 

 thread in connection with the other electrode is lightly 

 wound round the pulvinus. It is sometimes preferable, 

 for reasons previously explained, to make this contact with 



Fig. 67. — Two successive records, exhibiting identity of latent 

 period. Recorder ioo D.V. per second. 



glycerin. The connections are so made that the current 

 of the break-shock enters by the stem and leaves by the 

 pulvinus, the latter being thus the kathode. We shall 

 understand later the reason of this, in as much as the kathode 

 is the point of excitation. 



I now describe the record of an experiment (fig. 67) carried 

 out in summer for the purpose of determining the latent 

 period in a specimen of Mimosa. Stimulus was applied 

 at the point marked by the vertical line, and the upper of 

 the two records was the first taken. The vibrating-recorder 

 employed had been tuned to exactly 100 vibrations per 

 second ; successive dots therefore represent intervals of 



