The Sap — What Moves Through the Tree Unseen

Baobab wood is not hard. It is fibrous and spongy, closer to a packed sponge than to timber, and it holds water the way a cistern does. Through the dry months the tree is drinking from its own walls.

A cistern, though, is a still thing. A tree is not. Whatever the trunk holds has to keep moving out to the last twig, or the tree dies with a full trunk, which has to be one of the less dignified ways to go.

The part that never sits still

Sap is water with things dissolved in it. Sugar made in the leaves, minerals lifted out of the soil, hormones telling a bud when to open. On its own it has no shape worth keeping. What matters is that it goes somewhere.

Two channels carry it. One runs up through the wood, lifting water and minerals from the roots. The other runs in a thin layer just under the bark, moving sugar out from the leaves to whatever is growing. A few cells separate them, and both keep working in the dark without anyone checking.

Take a cutting from a houseplant and stand the stem in a glass of water. In a week or two pale roots push out of the cut end, in a room with no soil in it. The stem knew how to do that before you cut it. Water and light were enough to remind it.

Water goes up with no pump

A tree has no heart. Ask how water reaches a leaf thirty metres up and the honest answer is that nothing pushes it. Water evaporates out of the leaf, and the loss tugs at the column of water standing behind it. That column holds because water molecules cling to each other and to the narrow walls of the tubes they sit in, so it behaves less like a liquid and more like a rope.

On a hot still afternoon the water in a tall tree sits at a pressure lower than a vacuum. Let air into the column and that tube stops carrying for good. It is what a drought does before it kills anything, and it can happen in a single afternoon.

Not much sugar, and none of it locked away

Maple sap runs about two percent sugar. Boiling roughly forty litres of it yields one litre of syrup, and most of that work is removing water the tree spent months lifting. Nobody involved was making syrup except us.

The sugar channel runs under pressure. Aphids have learned to tap it: mouthparts fine enough to pierce a single cell, drinking until they are full and then dripping the surplus. The honeydew on a car windscreen in July is tree sap that has already been through an insect.

The bark is the only lock on that door, and it is thinner than it looks.

The argument between holding and giving

We have written before about what the tree keeps inside and the leaves it puts on and takes off. The sap sits between the two. Nothing rests. Everything is in transit, and the health of the whole thing depends on the transit staying open.

Most of us have a place where we stopped the flow. A grievance kept at exactly the right temperature. A kindness performed and then held up for inspection. It felt like storing something. It was blocking it.

We have done this. We suspect you have too, and that you can name the thing without much effort.

What is strange is the cost. A tree that sealed its own channels would not be resting. It would be dying slowly while looking sturdy, and the outside of a baobab gives very little away.

A practice for the week

Find one thing you are carrying that was never meant to stay with you. News that belongs to someone else, a skill you learned and never passed on, a worry you have been holding on behalf of a person who could hold it themselves.

Send it on this week, while it is still awkward to do.

The tree does not decide to circulate. It circulates, or it stops being a tree, and it has been doing this quietly through every dry season anyone has thought to count.

What is stuck in you that only needs to move?

The Eye watches. The Tree stands. The Delve awaits.