“Be part of history,” proclaims the copy on one ad. “Choose our national tree,” says another, explaining that the appointed tree will symbolize all of Amer ica’s trees.

Mount Vernon, the home of George Washington, is pictured in one ad surrounded by trees planted by old George himself. A leafy Central Park-like scene is shown in another with a quote from Teddy Roosevelt expounding on the importance of trees to the U.S.

The ads, part of a PSA series promoting The National Arbor Day Foundation’s national-tree voting drive, urge Americans to choose at the foundation’s Web site, arborday. org, or by mail. Votes can be cast until midnight on April 26; a winner will be named the next day, National Arbor Day.

Why now? “Conservation issues are a little more to the front right now,” said Gary Brienzo, foundation information director, adding that this is the first time Americans have been asked to provide input on a national symbol.

The ads, created by Omaha, Neb., agency J. Greg Smith, were sent to publications nationwide. There also are radio and TV spots.