Great overview!

What tools does a grammarian need? A brain helps, and so does a computer, but surely one of our most essential tools is some kind of diagramming system. How can we think about a sentence's structure, after all, without displaying it visually? Geographers have maps; mathematicians have equations; composers have musical notation; economists have graphs; and grammarians have trees.

It wasn't always so.

A Brief History of Diagramming Sentences