You’d think a tree is made of ground:
it stands in soil, it drinks the rain,
its roots go down and wind around,
and so we think it eats the plain.
But weigh the pot before you plant,
and weigh it when the tree is tall:
the soil has hardly changed. It can’t
have built the trunk, the boughs, at all.
The answer’s in the air instead.
Each leaf breathes in, through tiny doors,
the gas we breathe out, overhead,
the carbon from our yawns and roars,
and with the light that falls on it,
it splits the water from below,
and takes the carbon, bit by bit,
and stitches sugar, row by row.
The oxygen it doesn’t need,
from water, not the air, it frees;
and that’s the breath, and that’s the seed,
and that’s the timber of the trees.
So when you lean against the bark
and feel how solid it has grown,
remember it was air, a spark
of sunlight caught, and not of stone.
A small experimentCatch a leaf breathing out
- Put one leaf in each glass so it is fully under the water.
- Put one glass in bright sunlight and the other in a dark cupboard.
- After an hour or two, look closely at the surface of each leaf.
- Compare the two: which has more tiny bubbles clinging to it?
What's going on?
In light, the leaf keeps photosynthesising, splitting water and releasing oxygen, which collects as tiny bubbles. In the dark, photosynthesis stops, so you see far fewer. (Some bubbles can also come from air dissolved in the water, which is why the dark glass is the fair comparison.)