Continued from: Redwoods - The Role of Fog
The inside of a redwood tree contains lots and lots of water. This water transports nutrients from the roots to hundreds of feet up into the tree, where the leaves use those nutrients to manufacture sugars and starches. The only way to raise water that high is with a huge pump. How does the redwood tree do it?
The answer comes from Don Garlick, a geology professor retired from Humboldt State University. He states that evaporation from redwood leaves draws the liquid up through tiny micro-pores located in cell walls. The water and sap molecules stick together due to surface tension (that's what makes a drop of water bead up) and as long as the chain is not broken, a molecule will pull its neighbor along with it. As the tree grows, the water column extends with it.
According to Professor Garlick, this force has been measured to as much as minus 270 psi in a redwood tree. Cold water will start boiling (cavitation) at zero psi, but the redwood has developed resistance to cavitation because of the surface tension caused by the miniscule tubes. Continued.
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