Q.25 Fibers commonly formed in the secondary xylem of tension wood are termed:
1. Substitute fibers
2. Libriform fibers
3. Gelatinous fibers
4. Fiber tracheids
Tension wood forms gelatinous fibers in secondary xylem as a reaction to gravitational stress in angiosperms.
The correct answer is 3. Gelatinous fibers.
Question Breakdown
This MCQ tests knowledge of reaction wood anatomy, specifically fiber types in tension wood (upper side of leaning stems in hardwoods).
Option Explanations
| Option | Term | Explanation [Citation] |
|---|---|---|
| 1 | Substitute fibers | Found in primary xylem or rays; replace tracheids in some woods; not tension-specific. |
| 2 | Libriform fibers | Typical long, thick-walled secondary xylem fibers in normal angiosperm wood; high lignin. |
| 3 | Gelatinous fibers | Characteristic of tension wood; G-layer (S3) in fiber secondary wall is cellulose-rich, unlignified, gelatinous; generates tensile stress. |
| 4 | Fiber tracheids | Intermediate tracheid-fiber cells with bordered pits; common in softwoods, not tension wood. |
Why Gelatinous Fibers?
Tension wood corrects stem lean via contraction. G-fibers have microfibrils axially oriented in G-layer (high cellulose, low lignin), enabling shrinkage and tension generation.
Article Introduction
Understand fibers commonly formed in the secondary xylem of tension wood—gelatinous fibers (option 3)—essential for NEET, CUET botany on reaction wood anatomy. This guide explains G-layer structure, distinguishes from libriform/substitute/fiber tracheids, and covers gravitropic response mechanisms for exam success in xylem fiber types and wood formation.
Tension Wood Basics
Forms on upper side of tilted angiosperm stems; generates tensile force to upright growth.
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Normal wood: Libriform fibers (thick S2 wall, lignified).
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Tension wood: Gelatinous fibers with tertiary G-layer (unlignified cellulose, axial microfibrils).
Fiber Type Comparison
| Fiber Type | Location | Key Feature |
|---|---|---|
| Libriform | Normal secondary xylem | Elongate, thick-walled, simple pits |
| Gelatinous | Tension wood | G-layer swells/contracts, low lignin |
| Fiber tracheid | Softwood/transition | Bordered pits, conductive |
| Substitute | Primary xylem | Short, thin-walled |
Exam Relevance
CUET PG/NEET tests reaction wood vs normal wood fibers. Remember: Tension = Gelatinous (G for both).
