Here are some students, inspecting a Tilia species from two weeks ago. If you aren't familiar with Tilia tomentosa (Silver Linden) or Tilia cordata (Littleleaf Linden), then you may have encountered the trees recently and wondered if their tiny flowers were accountable for a subtly pungent fragrance.
Lindens are great trees and at first, it may be difficult to tell the difference between these two species, but the more you look at them, the more distinct they become. Littleleaf Linden, eponymously, has small, medium-green leaves and a horizontal branching habit. Silver Linden leaves are a darker with silvery undersides and the branches seem to sprout from the trunk like a bouquet of wildflowers. It's interesting -- at least to me -- to realize that the more pendulous habit of Tilia tomentosa is partly due to the fact that the leaves are larger and thus, heavier. The added mass, no doubt, pulls the branches closer to earth than Tilia cordata.
There is also American Linden (Tilia americana) or Basswood. Their leaves can be up to 8" long and the tree itself is much larger than the other two. Consequently, the habit of Basswood is even more pendulous than Silver Linden, and all the branches eventually touch the ground.
As you can see above, these leaves aren't as silvery as most Silver Lindens. But my bet is that this is still Tilia tomentosa, due to the bloom time and the fact the leaves are no more than 5" long.
There was once also a Tilia heterophylla, which has now been absorbed by the Tilia americana species. There's also the possibility that this is that plant.
If anyone has any concrete information on this tree (it's behind the Met, among the Saucer Magnolias and Corktrees), please let me know. I'd love to have a definitive ID.