**COMMERCIAL IMAGE** In this photograph taken by AP Images for Doubletree Hotels, Nathan Walker gets a closer look at the tree leaves at the "Exploring Trees Inside and Out" exhibit, presented by ... more 
**COMMERCIAL IMAGE** In this photograph taken by AP Images for Doubletree Hotels, Nathan Walker gets a closer look at the tree leaves at the "Exploring Trees Inside and Out" exhibit, presented by Doubletree Hotels and the Arbor Day Foundation at the Peggy Notebaert Nature Museum on Thursday, Oct. 21, 2010 in Chicago. (Jim Prisching/AP Images for Doubletree Hotels) less 
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Associated Press
Thu, Oct 21, 2010 5:37 PM EDT