WASHINGTON -- Michelle Obama held her first-ever book signing Tuesday at a Barnes & Noble store in downtown Washington for "American Grown: The Story of the White House Kitchen Garden and Gardens Across America." The first lady's well-received book is a guide to gardening as a family, based on lessons learned from her three years of overseeing the White House Kitchen Garden.

More than 150 people showed up and stood in line for hours on a rainy gray morning, many of them mothers with school-aged children.

"This is my very first book and my very first and probably only book signing," said the first lady, who seemed genuinely excited about autographing her own work. Before she began, Obama double-checked with an assistant that she was writing her name on the right part of the book. "I'm so very proud of this product, and it's everything I would have imagined," she beamed.

The first lady stressed the importance of involving children in growing or choosing what they eat, explaining that it was only when she did this with her own daughters that "they really accepted [healthy diets] much more."

During her five-minute remarks, she was flanked by students from two Washington public schools, Bancroft Elementary and Harriet Tubman Elementary. Both schools have partnered with the White House to allow students to volunteer in the White House Kitchen Garden.

On the heels of an all-out media blitz last week, including the first lady's appearance on "The Daily Show With Jon Stewart," Obama's book has rocketed to the top of the New York Times Best Sellers list for hardcover advice books.

Designed to appeal to both young readers and their parents, "American Grown" includes dozens of full-color photos and offers food-related anecdotes about the first family. The book seeks to further one of the first lady's signature initiatives: combating childhood obesity. Obama writes of growing up on the South Side of Chicago, where "vegetable gardening wasn't exactly a common pastime." Years later, a pediatrician advised her to make sure her two young daughters ate more vegetables.

The first lady also reveals that she began thinking about the White House Kitchen Garden in early 2008, long before her family moved to Washington, when Barack Obama was still a junior senator battling Hillary Clinton for the Democratic presidential nomination.

Once the family arrived at 1600 Pennsylvania Ave. in January 2009, plans came together quickly, and the first lady broke ground on the garden that April with the help of local elementary school students. Since then, the garden has expanded to include, among things, beehives on the White House lawn and heirloom beans first cultivated by Thomas Jefferson at Monticello.

There's more to "American Grown," however, than stories and photos from the Obamas' garden. The coffee-table book also highlights a number of urban vegetable gardens around the country, from Maui to New York City, and serves up recipes from White House chefs.

Below, more on U.S. first ladies and their charitable causes:

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  • Dolley Madison

    Dolley Madison, wife of President James Madison, was the first First Lady to formally associate herself with a cause, <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=4" target="_hplink">according to Firstladies.org</a>. Madison helped found an orphanage for young girls in Washington, D.C., and maintained a lifelong connection to the organization.

  • Harriet Lane

    Although she was the niece of bachelor President James Buchanan and not his wife, Harriet Lane was nevertheless considered the First Lady of the Buchanan White House, <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=16" target="_hplink">according to Firstladies.org.</a> But, similar to other benevolent wives of our presidents, Harriet committed herself to two underserved populations that needed help -- Native Americans and children.

  • Ellen Axson Wilson

    Ellen Axson Wilson, the first wife of Woodrow Wilson, died young, but made a big impact during her short life, <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=28" target="_hplink">according to Firstladies.org</a>. She joined a campaign to get rid of the slums in the Washington, D.C. area, and advocated for improved housing and child labor laws.

  • Florence Harding

    When President Warren Harding was first elected to the U.S. Senate, his wife began advocating for the rights of returning World War I veterans. <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=30" target="_hplink">According to Firstladies.org</a>, Florence Harding launched the "Lest We Forget" Week to encourage donations of books and clothing to returning soldiers. She was also known to pick up wounded veterans on the street who needed a ride.

  • Grace Coolidge

    First Lady Grace Coolidge, the wife of President Calvin Coolidge, had always been interested in education -- especially for the deaf. During her husband's presidency, Grace became a trustee for the Clarke School for the Deaf, and was also involved with the American Red Cross during World War I, <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=31" target="_hplink">according to Firstladies.org</a>.

  • Lou Henry Hoover

    Before becoming First Lady, Lou Henry Hoover worked as an organizer for the American Red Cross' Canteen Escort Service, which transported wounded soldiers home during World War I. Her support for the troops was honored by King Albert I of Belgium, <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=32" target="_hplink">according to Firstladies.org</a>.

  • Eleanor Roosevelt

    During World War II, Eleanor Roosevelt supported the troops by volunteering with the American Red Cross, where she handed out cups of coffee, newspapers, sandwiches, candy, and cigarettes to soldiers heading out to army camps and ports, according to the <a href="http://www.redcross.org/museum/history/eleanorR.asp" target="_hplink">American Red Cross.</a> "I loved it," the organization quoted her having said. "I simply ate it up."

  • Barbara Bush

    After her son Neil was diagnosed with dyslexia at a young age, First Lady Barbara Bush began championing the cause when she founded the <a href="http://www.barbarabushfoundation.com/site/c.jhLSK2PALmF/b.4344531/k.BD31/Home.htm" target="_hplink">Barbara Bush Foundation for Family Literacy</a>, according to <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=42" target="_hplink">Firstladies.org</a>.

  • Hillary Clinton

    While serving as First Lady, now Secretary of State Hillary Rodham Clinton led the effort on the Foster Care Independence Bill, which helped older unadopted kids transition successfully into adulthood, <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=43" target="_hplink">according to Firstladies.org</a>.

  • Michelle Obama

    Still enjoying her role as First Lady to President Barack Obama, Michelle Obama has been vocal about three issues during her husband's administration: Helping working mothers, providing support to military families, and encouraging voluntarism, <a href="http://www.firstladies.org/biographies/firstladies.aspx?biography=45" target="_hplink">according to firstladies.org</a>.

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