An interconnected system in plants that consists of all the cell walls, the water that exists in them (the cell wall is composed of cellulose fibres, between which are spaces filled with water), the intercellular spaces, and dead cells such as vessel elements and tracheids. The movement of water (and dissolved ions and solutes) through the apoplast is known as the apoplastic pathway. This is the main route by which water taken up by a plant travels across the root cortex to the endodermis (see casparian strip). See also phloem loading; phloem unloading. Compare symplast.