SUMMARY.
The very complex type of nyctitropic movement of the primary petiole of Mimosa results from the combined effects of thermo-geotropism and phototropism.
With the exception of a small portion of the curve in the evening, the diurnal curve of Mimosa is similar to the standard thermo-geotropic curve, where the leaf exhibits an erectile movement from thermal-noon to thermal-dawn, and a fall from thermal-dawn to thermal-noon.
Investigations show that the leaf of Mimosa has an autonomous movement of its own, which persists throughout twenty-four hours.
The torsional response of Mimosa exhibits a diurnal variation similar to that exhibited by the leaf in normal position.
The leaf of Cassia alata exhibits a diurnal movement of the same type as that of Mimosa.
The spasmodic fall of the leaf towards evening is not due to the increased mechanical moment caused by the forward position of the sub-petioles. The record of the leaf with amputated sub-petioles exhibits the sudden fall in the evening as that of the intact leaf.
The evening fall of the leaf of Mimosa is shown to be due to the post-maximum after-effect of light, which causes an 'over-shooting', the leaf undergoing a fall below the position of equilibrium.
[45] Blackman and Paine—"Annals of Botany" January 1918.