DIURNAL MOVEMENT OF MIMOSA 583 



periodic increase during the fall of temperature from 

 afternoon till next morning, and a diminution during 

 rising temperature from morning till afternoon, A sudden 

 diminution of torsion occurs at about .') p.m. due to the 

 disappearance of light. The torsional record is, to all 

 intents and purposes, a replica of the record of periodic 

 up and down movements of the leaf. 



This method of torsion has several advantages over the 

 or<linary method. First, the petiole being supported by 

 the loop of wire, the weight of the leaf has no effect on 

 the curve of response. In the second place, the periodic 

 variation of turgor of the stem, as suggested by Millardet, 

 will not in any way affect the record. Variation of 

 turgor can only cause a swing to and fro, in a direction 

 perpendicular to the plane which divides the pulvinus 

 into upper and lower halves; it can in no way induce 

 a torsional movement, or a variation of the rate of that 

 movement. 



The automatic pulsation of tJie leaf of Mimosa. — Tlie 

 occurrence of the pulsatory response in the morning record 

 of Mimosa led me to search for multiple activity in 

 the response of the pulvinus. I have in my previous 

 investigation on the electric response of Mimosa obtained 

 multiple series of responses to a single strong stimulus. 

 Blackman and Paine have recently shown that an isolated 

 pulvinus of Mimosa exhibit multiple mechanical twitches 

 under excitation.* 



Even under normal conditions, the sprouting young 

 leaves in March, as already stated, exhibit automatic 

 pulsations throughout the day and night ; in older leaves 

 tuned to diurnal periodic movements, these natural pul- 

 sations are more or less suppressed. But in the forenoon, 

 several pulsations are exhibited even by the old leaves. 



* Blackmaa and Paine— •' ^naals of Botany " January 11U8. 



