for the mathematically inclined

square roots

These two photos are of a tree that grows alongside the cycle track that runs parallel to Pak Wo Road in Fanling. The brick paving, which has been laid in a single basket-weave pattern, has constrained the directions in which embryonic roots of the tree near the surface can grow, and all changes of direction are right-angles.

In the bottom left-hand corner of the second photo, the paving changes to a series of parallel stretcher courses, which explains the tight turn of the root nearest the camera through two right-angles.