Sometimes I try to imagine the shape of the living parts of trees. Since trees grow outward (those rings you see in a cross-section), and leave the old layers behind as dead structure, the living part is a thin green skin, stretched over the whole trunk and branches, just under the bark. If you removed the bark, and all the wood, and filled what was left with air, a tree would resemble some green thing made from those balloons tied into animals and headgear at childrens' birthday parties. Another way to think about trees is that they contain, inside each other, all of their former selves. An old oak might contain within itself the shape it had two hundred years ago.
A tree is like matryoshka, those Russian nesting dolls (photo credit to RedKen on Flickr). If you could peel it, like an onion, you could take it's shape back through time, year by year, except for lost limbs. Each layer is the petrified former living tree.
And the tree in leaf is hollow and layered in another way. Leaves grow mostly on the very outside of the leafy crown, in order to catch the sunlight. What any tree climbing child discovers is that the hearts of trees are wonderfuly open, and I recall as a child feeling like I was climbing up into the globe of a hot air balloon when I pulled myself up the sugar maple where our bird feeder hung.
I would sit in one spot in the branches and dream. Through gaps in the leafy sphere I would look over the old house, over the Roelof Jansen Kill, towards Turkey Hill. I used to take a box of Sunmaid raisins up there after school, and I would sit high in the leafy ball and eat them. The taste of raisins can still remind me of the hard round pressure of tree limbs under my hands and feet. I think of all those decades of layers of wooden images of the tree as it grew, holding me up in my lofty perch, a wood filled living balloon inside a leafy balloon, and myself in between.
Painting above is from my art website - more images here.