Question
Explain root pressure theory and its limitations.
✓
Answer
- Root pressure theory is proposed by J. Pristley.
- For translocation of water, activity of living cells of root is responsible.
- Absorption of water by root hair is a constant and continuous process and due to this a hydrostatic pressure is developed in cortical cells.
- Owing to this hydrostatic pressure i.e. root pressure, water is forced into xylem and further conducted upwards.
- Root pressure is an osmotic phenomenon.
Limitation of this theory:
- Not applicable to tall plants above 20 metres.
- Even in absence of root pressure ascent of sap is noticed.
- In actively transpiring plants, root pressure is not developed.
- In taller gymnosperms, root pressure is zero.
- Xylem sap is under tension and shows negative hydrostatic pressure.
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