bio

Turgor pressure

The water pressure inside a plant cell pushing out against its wall, making it firm — what keeps leaves and stems from wilting. A cell needs enough turgor to expand and grow. At the top of a very tall tree the water is pulled so taut that turgor drops too low for the leaf cells to expand: the topmost leaves come out tiny, dense, and shrivelled. That is the sign a tree has reached the limit of its height.