A Ponderosa Pine needle scanning electron microscope image. What we see is that the xylem (in red) embolizes as the leaves get more dehydrated. a) fully hydrated at minus 112 degrees Fahrenheit (minus... more 
A Ponderosa Pine needle scanning electron microscope image. What we see is that the xylem (in red) embolizes as the leaves get more dehydrated. a) fully hydrated at minus 112 degrees Fahrenheit (minus 80 degrees Celsius (cryoSEM); b) fully hydr less 
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LiveScience.com | Photo By Dan Johnson, Duke University
Tue, Mar 12, 2013 12:00 PM EDT