In roots, most of the water flows through

The correct option is Apoplast.

In plants, water absorption and transport through the root cortical cells occur via two major pathways: the apoplast pathway and the symplast pathway. The apoplast pathway is the primary route for water movement in the root cortex because it offers the path of least resistance.

Understanding the Apoplast Pathway:
1. Non-Living System: The apoplast consists of the non-living parts of the plant tissue, which includes the cell walls and the intercellular spaces between adjacent cells.
2. Low Resistance to Flow: Unlike the symplast pathway (where water must cross selectively permeable cell membranes and travel through the cytoplasm via plasmodesmata), the apoplast pathway does not involve crossing any cellular membranes within the cortex. This absence of membrane barriers means water can move freely and rapidly by bulk flow and diffusion.
3. Continuous Movement: Because the cell walls are hydrophilic and porous, they act as a continuous channel through which water can easily seep without entering the living cells.

The Endodermal Boundary:
Although the majority of water flows through the apoplast across the root cortex, this pathway is eventually blocked at the endodermis. The endodermal cell walls contain a band of suberized matrix called the Casparian strip, which is impermeable to water. At this boundary, water is forced to cross the cell membrane and enter the symplast pathway to reach the vascular cylinder (xylem). However, up to the endodermis, the apoplast remains the dominant pathway for water transport.