Study
Xylem Structure and the Ascent of Sap
Tyree, Melvin T.; Zimmermann, Martin H.
Springer, 2002
A monograph on the structure of wood and the physics of water movement through it, covering the cohesion–tension mechanism, cavitation, embolism repair and the trade-off between transport efficiency and safety.
- Studied in
- Tracheophyta
- Sample size
- monographic synthesis of xylem structure and water transport
Water rises through xylem under tension generated by evaporation from leaves, held together by the cohesion of water. Wide vessels move water efficiently and cavitate readily; narrow ones are safer and slower, and this trade-off shapes wood anatomy across climates.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
The ascent of sap is a passive, evaporation-driven process operating under negative pressure, constrained throughout by the risk of the water column breaking.
How NatureHQ reads it
Reference consensus for the mechanism behind almost every tree question people ask. The counter-intuitive part is worth stating plainly: a tree does not push water up, it pulls, and the water is under tension — stretched, not compressed — the entire way. That single fact explains height limits, why drought kills trees, why ring-porous and diffuse-porous woods look different, and why a severed trunk hisses.
- A synthesis across an enormous range of species and conditions.
- Embolism repair mechanisms remain actively debated and have moved since publication.
- Measurement of xylem tension is technically contested at the extremes.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Trees
A tree has no pump. Water is pulled up, stretched, by evaporation from the leaves
Trees
Trees stop growing at around 120–130 m because water cannot be pulled higher
Oak trees
An oak gall is grown by the oak — the wasp only supplies the instructions
Trees
Water can be lifted to the top of a tree without anything alive doing the lifting.
Wood
A trunk grows in one thin layer just under the bark. Everything inside it is finished.
Wood
The centre of a big trunk is dead, and the tree is fine — a hollow tree can be perfectly healthy.
Published by: Springer journalsPublished in a Springer journal.
doi.org/10.1007/978-3-662-04931-0
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-10.