The phenomenon you are referring to is called plasmolysis. Plasmolysis occurs when a plant cell loses water through osmosis, causing the cell membrane to shrink away from the cell wall. This process is typically observed when plant cells are placed in a hypertonic solution, which has a higher concentration of solute particles than the cell. As water moves out of the cell in an attempt to equalise the concentration on both sides of the membrane, the cell membrane detaches from the cell wall and the cell collapses. Plasmolysis can lead to permanent damage to the cell if it is not reversed.