IRRITABILITY OF PLANTS 143 



the vertical line in the record. The successive dots are 

 at intervals of two hundredth part of a second, and the 

 leaf-movement began at the fifteenth dot after the shock 

 (Fig. 12). The perception -time of the plant is thus 0-75 of 

 a second. When the plant is fatigued, its perception- 

 time becomes very sluggish : when excessively tired, it tem- 

 porarily loses its power of perception. In that condition 

 the plant requires at least half an hour's absolute rest to 

 regain its equanimity. 



For some purposes, however, the Resonant Recorder 



FIG. 12. Record for determination of the latent period of leaf of Mimosa. 

 Shock given at vertical line ; successive dots at intervals of 0-005 

 second. 



has its limitation. It measures movements which are 

 exceedingly quick ; there are, however, other movements 

 which are relatively slow, and Bose still needed an instru- 

 ment which could take slower records, lasting for hours 

 and days. Moreover, some movements may be so slight 

 and weak that even the recording system just described 

 being necessarily of magnetisable metal though at its 

 finest may be too heavy for the excessively limited 

 mechanical power of certain plant -movements. 



Hence, instead of the writer oscillating so many times 

 per second, he now set the smoked glass plate oscillating, 

 to come up periodically against the point of the writer- 

 The oscillation can now be as slow as we please, since by 

 various ingenious adaptations of clockwork we can obtain 



