The idea behind this photograph is to portray the "expansiveness" of an essential submodule. To use a linguistic metaphor, an essential submodule N of a module M is a submodule that has its fingers in the pots of every one of M's submodules: if L is any nontrivial submodule of M, then N and L must have a nontrivial intersection. N need not contain many elements, however; its significance in M is due to its "density" in M, so to speak, rather than to its size. This photograph attempts to convey this density: the tree (our submodule) fills the picture (our module), leaving no room in which other submodules can play without its leaves getting in the way..