Details of the Casparian strip. Image from Purves et al. Tracheids are long, tapered cells of xylem that have end plates on the cells that contain a great many crossbars. Tracheid walls are festooned with pits. The functional diameter of vessels is greater than that of tracheids.
Water is pulled up the xylem by the force of transpiration , water loss from leaves.
Mature corn plants can each transpire four gallons of water per week. Transpiration rates in arid-region plants can be even higher. Water molecules are hydrogen bonded to each other. Water lost from the leaves causes diffusion of additional water molecules out of the leaf vein xylem, creating a tug on water molecules along the water columns within the xylem. The loss of water from the root xylem allows additional water to pass throught the endodermis into the root xylem.