being done the green leaflets were alternately subjected to strong light and to darkness, -care being taken that the pulvinus was shaded all the time. The alternate action of light and darkness on leaflets induced no variation in the uniformity of response. This shows that the observed variation of excitability in Mimosa under the alternate action of light and darkness is not attributable to the photo-synthetic processes.
I next took a petiole-pulvinus preparation from which the sub-petioles bearing the leaflets had been cut off, and placed it in a room illuminated by diffused daylight. The normal responses were taken, the temperature of the room being 30^ C. The room was darkened by pulling down the blinds, and records were continued in darkness. Th'^ temperature of the room remained unchanged at 30° C. It will be seen from records given in Fig. 40, that in
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Fig. 40.— Stimulating action of light, and depressing action of darkness. Horizontal line below represents period of darkness.
