The symplast is one of the three methods of radial transport of water and solutes in plant tissue.
The symplast consists of all of the cellular cytoplasm in a network of small tunnels which perforate the walls between the cells: the plasmodesmata.
After penetrating a cell, water and solutes can travel through this channel, but also leave it to join the apoplast or successively cross the plasma membranes and the pectin-cellulose walls.
Diagram of radial transport channels in plant tissues. The symplast channel (in dark green) is traced by the network of cytoplasm, interconnected by the plasmodesmata. © Jackacon, Wikimedia public domain