The 50th oak tree was planted today at the September 11th Memorial Plaza in the World Trade Center site.
The 30-feet-tall swamp white oak was lowered into position in the Downtown Manhattan plaza, where it will be one of 400 trees surrounded two water pools built in the Twin Towers' original footprints.
Mayor Michael Bloomberg was on hand for the planting, calling it a small but symbolic step.
"It shows that the World Trade Center site is progressing, in particular the memorial, which will be done on time and on budget," said the mayor. "There'll be one corner that won't be done because the [Santiago] Calatrava[-designed transit] terminal is going to go under it, but we fully expect that on the 10th anniversary of this terrible tragedy that struck America, that was against democracy, against freedom-loving peoples all around the world, people will be able to walk on the plaza."
The memorial's oak trees have been growing in a nursery in New Jersey since 2007. The plantings began this August.
Some 250 trees are expected to have taken root by the 10th anniversary of the terrorist attack.