COMPANION NOTES: the green breath of leaves

Remembering the mutual yet invisible relationship between the body and the plant world, and why it’s good to get better at watering your houseplants.

In a way, plant breathing starts from the most common thing that plants share, their greenness. This arises from a pigment in their cells called chlorophyl which has the astonishing ability to capture energy from sunlight. Think about that and the effort of human engineering involved in solar panels and you can’t fail to be amazed.

There are other leaf pigments as we know from observing the shift from summer to autumn, that time of year when deciduous trees and shrubs enter their resting season. Less energy is required, less sunlight is available, and hence the leaves turn from green to gold, from copper to red, before falling. Mary Oliver has a beautiful way of contemplating this in her poem Song for Autumn (from the collection New and Selected Poems Volume 2):

Don’t you imagine the leaves dream now
how comfortable it will be to touch
the earth instead of the
nothingness of the air and the endless
freshets of wind?

Anyway, let’s come back to a little bit of science. The simple equation of light from the sun, plus water from the roots, plus carbon dioxide/CO2 (and water) from the atmosphere, means a plant has all it needs to create the glucose required for its cellular functions. What is not needed by the plant is the oxygen which it has split from the water molecules during photosynthesis and it ‘exhales’ this, so to speak, into the air where our own inhalation awaits. The interface for gas exchange on the leaf is through tiny pores called stomata which allow CO2 to pass in and oxygen to pass out. We might liken this whole process to our own primary respiration, the breath that connects the inner environment of the plant ‘body’ with the outer environment of the world.