Final answer:
The symplast refers to the interconnected cytoplasm of neighboring plant cells, allowing materials to be transported between cells via plasmodesmata.
Step-by-step explanation:
The cytoplasmic continuum connecting neighboring cells is called the symplast. In the context of plant biology, the symplast refers to the collective volume of the cytosols of all cells, which is contiguous because all cells are interconnected by plasmodesmata. These are membrane-bordered cytoplasmic threads that run between cells, allowing for the direct movement of solutes, signal molecules, and water. Unlike the Casparian strip, which is a waxy barrier in the apoplast that forces substances to cross a cell membrane to enter the vascular cylinder, plasmodesmata facilitate transport between cells without such filtration.