Abstract:In order to understand the nyctinasty of leaves and flowers of Oxalis corniculata, the leaf pillows and receptacles were studied by semi-thin section. The results showed that the leaves were completely closed after dark treatment, and three leaves were tightly closed downward with the leaf axis as the axis. The petals were completely closed and spiraled into bundles under dark for 8 hours, and the calyx clung to the spiral petals but did not spiral. The cortical parenchyma cells on the flexor side contracted and the parenchyma cells on the extensor side expanded when the leaf was opened. When the leaf was closed, cortical cells on the flexor side expanded, epidermal cells on the extensor side and parenchyma cells on the 3-5 layers of outer cortex contracted. When the flower closed, the five vascular bundles at the base of the container contracted and merged into two distinct vascular bundles, and the cell walls were thickened. Cells swell at corner of receptacle. Therefore, the contraction and expansion of flexor and extensor muscle cells in the leaf occipital control the nocturnal motion of the leaves of O. corniculata. The nocturnal motion of flowers is mainly related to the enlargement and contraction of the vascular bundles at the base of the receptorum and the cells at the corner of the receptorum.