In the early C17th, a century before the masons raised the mauve rubblestone walls of St.Edith’s, a wordsmith merged the Latin Ab (off), with Scindere (to cut), to create abscindere, or abscissio, and thence today’s abscission.
An action noun, meaning a cutting off; a breaking off.
But first, an explanation.
Principally because, for most temperate plants, leaves aren’t capable of surviving frosts. So the first significant frost will kill all leaves, which would fall from the plant, or just collapse in the case of many annuals or herbaceous perennials. For many deciduous woody perennials – shrubs and trees, planned ageing, or senescence of the leaves is just a normal precursor to leaf abscission and loss.
The plant prepares, annually, for the onset of winter by altering the complex biochemistry inside the leaf. Protein synthesis reduces, protein levels within the leaf are reduced due to enzymic protein breakdown, respiration declines, and the rate of carbohydrate breakdown also increases. RNA is broken down, and finally, the photosynthetic green compound chlorophyll, is degraded. The breakdown products of all this biochemical change are rapidly transported from the ageing leaf, and into the other permanent parts of the plant (trunk, stem, and roots), for upcycling in due course.
These complex changes are coordinated by plant hormones, in particular ethylene and abscidic acid. To enable abscission to take place, a special layer of cells (the abscissional layer), develops at the base of the leaf’s stem, or petiole. As senescence proceeds, increasing levels of ethylene stimulate these abscissional layer cells to respire faster, and causes the cells nearest the stem to increase in size. At the same time, cells in the abscissional layer furthest from the stem, begin to break down polysaccharides in the cell walls, again under hormonal influence, thus weakening their strength.
The pressure between the enlarging cells closest to the stem, and the weakened cell walls nearer the leaf eventually causes a split to develop, and the leaf falls to the ground. So the combination of senescence and abscission is a great way for deciduous plants to recycle carefully produced nutrients before the chill of winter would rob the plant of this material.
First to Hergest Croft. On the very borders of England and Wales. And with good fortune, timed to perfection, for a clear blue sky, sunny day. Surprisingly the changes here were perhaps two weeks ahead of our own plants. Stunning vistas, and on this late October day, fewer than a dozen cars in the car park, around lunch. If you’ve never been, plan a trip for next year – particularly for late spring, or autumn. A visual treat, only limited by the shortened days at this time of the year.
Then for the third time in two years, a different autumnal trip. I can now predict with some accuracy, the relative timing of leaf colour change and abscission in our own woody plants, and value them all for their beauty, and sequential guiding of seasonal change.
Under more clear, cold, blue skies, another life remembered.
The wedding church revisited. Too soon. For such raw emotions.
Cambridge Blue. And White.
A whole life distilled, such clarity, in ten short, memorable, memorial tales.
How was that done?
An hour of favourite music, to contemplate
Amongst the hushed banter with closed eyes,
As pews filled and tears welled.
Much time to think.
Emotionally drained, we park up at the Dolaucothi,
A quick supper. Too late for cooking food at home.
” Gosh, You’re looking very smart. Had a special day?”
Asks bubbly geordie Jo.
We mumble the ‘f’ word.
In shared solitude, save serious bikers,
As our third trip, in a long week, we’d headed to the National Botanic Garden of Wales, just in time to be excitedly ushered towards the pupae cabinet, by the young staff scientist in the tropical house, where a butterfly was trying to emerge from its chrysalis, tip superglued on a thin dowel, and hanging vertical, between already empty, fragile, imprinted, chitin cists.Willing it on, the three of us are gripped, misted lenses censoring records, as after all the alchemy of complex soups, within the crisp retaining pupal cage, the rubbered larva has dissolved, reformed. The laced butterfly poised.
Struggle out within a few minutes, more than just those flailing legs, little butterfly, or use up your energy supplies, exhaust yourself, and succumb, before your deformed crumpled wings have ever even inflated.
Click below, if you’ve never heard this reflective piece of piano music before.
And if you’ve got the data allowance, and know it well, then click anyway! A recently rediscovered and enjoyed musical postscript, courtesy of Stephen Hough, and Stephen Baggaley.