On a hot summer day, one large tree can pump over a thousand gallons-that's four tons-of water from the ground to its leaves. The water is collected from the soil through the roots. But the real work of pumping four tons of water, often 100 feet into the air, occurs at the top of the tree. The water is suctioned toward the treetop by three remarkably efficient mechanisms-capillary flow, osmosis, and vacuum pressure. Osmosis and capillary action act in concert to move the water partway to the top of the tree, but the real driving force is pressure differential created by the leaves within the vessels of the tree. This pressure differential is a result of water evaporating from the leaves of the tree, creating a suction throughout the vessels. This suction (measured as low as 1/20 of atmospheric pressure) helps to draw water from the roots all the way to the top of the tree. If you were to cut one of these vessels, you could actually hear (using extremely sensitive equipment) a hissing sound as air rushed back into these vessels.

The engineering excellence of this silent pumping system, which efficiently delivers moisture to the very top of trees, is a not-so-silent witness against the idea that chance evolutionary processes (such as mutations) could have developed it.

From A Closer Look at the Evidence by Kleiss, January 4.

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