In a root endodermis, passage cells are present

Passage cells are those endodermal cells with casparian thickenings only on the radial walls but not tangential walls. They allow the passage of mineral water collected in the cortex into xylem. Since mineral water has to enter into the xylem, they are present opposite to xylem. Such endodermis acts as water dam for the entry of water from cortex into the root xylem.