Treepots

Came across an unusual tree somewhere near Great Portland Street tube station the other day. The unusual was not anything to do with what sort of tree it was, which I did not notice, but in the manner of its planting (see diagram left).

The tree (B) appeared to have been planted in an oval, masonry container (A), I think brick, standing maybe two and a half feet above pavement level. The container had been entirely filled by the roots of the tree, which were also poking through the odd fissure in the masonry, fissures whose primary purpose appeared to be as containers for fag ends. The question was, what happened at (C)? Was the container open to the ground beneath or was the tree contained by the container?

Containment seemed a bit unlikely given the size of the tree, with a trunk more than a foot in diameter. On the other hand, why would you plant an open bottomed masonry container on the pavement? I shall have to return for closer inspection and photographs.