Osmosis is what causes a symplastic pathway across the cytoplasm of cells. The plasmodesma are small thin strips which allow a strand of cytoplam to pass through. This causes a continuous column to be formed between the root-hair cell to the xylem.
Water enters the root-hair cell by osmosis. This makes the root-hair cell have a higher water potential than the first cortical cell, which causes water to move down a concentration gradient into the first cell. As the first cell now has a higher water potential than the next cell, water is drawn out of the first cell into the second cell down a concentration gradient by osmosis. At the same time, as the water potential in the first cell has dropped due to passing water to the second cell, more water is drawn out of the root hair cell, and the process starts again.
This causes a water potential gradient to be set up across all the cells of the cortex, which carries water along the cytoplasm from the root-hair cell to the endodermis.