Water Absorption by Needles of Ponderosa Pine Seedlings and Its Internal Redistribution

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Abstract
The tops of two-year-old ponderosa pine seedlings were exposed to a con-tinuous mist-spray after their roots had been sealed into either empty flasks or cans of soil. Under these conditions water moved back through the plant and out through the roots only when the temp. in the flasks was allowed to fluctuate. Those plants whose roots had been sealed in soil failed to show any backward movement of water out through their roots. Backward movement of water through these plant appears to result from a vapor pressure gradient and is not due to any "active" secretive force within the plant itself. Prolonged survival of pine seedling in soil at the wilting point when tops receive dew at night, as reported elsewhere, cannot be explained on the basis of water movement back out through the roots into the surrounding soil. The seedling under such conditions is able to live longer because of a re saturation of needle tissue and a concomitant reduction in amount of moisture removed from the root system.