This method of torsion has several advantages over the ordinary 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 the leaf of Mimosa._--The 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.[44] [44] Blackman and Paine--"Annals of Botany" January 1918. 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 pulsations are more or less suppressed. But in the forenoon, several pulsations are exhibited even by the old leaves. The question may now be asked: Why should the pulsations occur preferably in the morning? In connection with this I shall refer to the suppression of the pulsatory activity of _Desmodium gyrans_ when the leaflet was pulled up by the action of light (cf. Fig. 188). The leaf of _Mimosa_ executes a very rapid movement of erection at night, and the natural pulsations are thereby rendered very inconspicuous. These pulsations may, however, be found in the night record of young leaves. The general occurrence of pulsations in the forenoon is probably due to the fact that the resultant force which causes the down-movement is at the time relatively feeble--the operative factors being: (1) the action of the rising temperature which induces down-movement, and (2) the action of light which in the forenoon opposes this movement. It will thus be seen that the forces in operation in the forenoon are more or less in a state of balance, hence conditions for exhibition of natural pulsations are more favourable in the morning than in other parts of the day.