concept

Cohesion-tension

The mechanism by which a tree lifts water without a pump. Water evaporating from the leaves at the top pulls on the water just below it, all the way down an unbroken thread running through microscopic pipes in the wood. Water molecules cling to each other strongly enough that the whole column holds together under tension — like a rope pulled from the top. The higher the tree, the greater the tension, and past a threshold the column snaps: this is what sets the maximum height of any tree.