Pigment ink on hot press acid free drawing paper, 5 × 8 inches.
The Cayley tree is a mathematical object related to a Bethe Lattice (see the wikipedia article for an overview here: http://en.wikipedia.org/wiki/Bethe_lattice). It’s essentially a branched structure. Each node joining the branches in the “tree” has three branches emanating from it (think of it as a trunk that forks into two branches at the node). Each branch terminates at another node which also branches. A smooth plane has two dimensions and a smooth line has one dimension, but a Cayley tree has an intermediate dimensionality. This can be useful for certain types of calculations: where a fractal surface either better reflects the physics of the system, or where the symmetry of the Cayley tree simplifies the physics and/or math.
In “Variation on a Cayley Tree” some liberties were taken with the strict branching geometry and topology of the mathematical object, in order to map it onto a form that actually resembles a tree.