[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/03/17/art.ireland0317.gi.jpg caption ="President Obama and Irish Prime Minister Brian Cowen take part in a Shamrock Ceremony March 17, 2009."](CNN) - It was a balmy March day in Washington as the Irish ambassador to the U.S. headed to the White House. He carried a small gift for the president: a box of Irish shamrock, in honor of St. Patrick's Day.
The year was 1952. The president, Harry Truman, was out of town. So the ambassador, John Joseph Hearne, dropped off the shamrock and went on his way.
Such was the inauspicious inception of what's become a perennial event: the St. Patrick's Day shamrock ceremony, in which the U.S. president receives a cluster of Ireland's most famous greenery on the feast day of Ireland's patron saint.