The Minus Touch
It's a familiar science experiment. You place a stalk of celery into a beaker of dyed water. Over time, the dye moves up the vessels of the stalk and enters the green leaves, turning them red. Although it's easy to see what happened, the mechanics underlying the rise in water are obscure. In spite of what certain textbooks declare, no one really knows how water is drawn up the vessels of plants! The traditional explanation involving negative pressure is being replaced by concepts of metastable states and fluid tensile strength.
published online March 1, 2003
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