- 10 年前最愛解答
Sorry I studied Biology in English, hope you can understand.
Support in plants is provided by turgidity of thin-walled cells (e.g. cortex cell) and rigidity of thick-walled cells (e.g. xylem vessels).
When water supply is adequate (有水的), xylem has a higher water potential than the cells in the cortex (皮層) and pith (髓). Therefore, water moves from the xylem into these cells by osmosis. The cells become turgid and press against each other. The turgidity makes the whole stem strong enough to stand upright.
However, when water supply is inadequate, or when a plant has lost too much water, the cells in the cortex and pith will become flaccid. They can no longer support the stem and the plant wilts (凋謝). If this wilted plant takes up enough water shortly, the cells will become turgid and the plant will once again stand upright.
In conclusion, it is mostly because the cells in the plants lose water and cannot press again each other to give pressure, hence the plant does not gain support to stand upright, and it wilts.