Illustration of a plasmodesma. Plasmodesmata are channels in plant cell walls that connect adjacent cells. They allow transport and communication between the cells. The outer layer of the plasmodesma is a continuation of the cell membrane. Within this is the cytoplasmic sleeve, an extension of the cell cytoplasm through which most molecules move. It also contains structural proteins (lighter green). At the centre of the plasmodesma is a desmotubule (pink), an extension of the smooth endoplasmic reticulum of the cell.