Last week I didn't post, because of the mosque massacre, and my city is grieving. I won't dwell on it. But when horrific events shake you up, being mindful might help you accept your feelings and explore them so you can move on when you're ready. Part of being mindful is paying attention to your surroundings, and at the moment in Christchurch my surroundings are doing autumn.
Autumn is my favourite season. The cooling air brings relief from the inescapable heat of summer. The fire, which has slept since November, can flicker into life again. Apples and pears are available for jam and pie making. Mushrooms spring from the ground after rain. The trees look their best in red and yellow. Autumn is about fruiting and dying; it's a good job that plants die gracefully and quietly, or autumn would be a disturbing season.
Autumn in New Zealand carries a bittersweet note, as most native trees are evergreen. The autumn colours of Christchurch are a testament to how much Europeans have destroyed the native habitat here. I wish the City Council would replace more of the exotic deciduous trees with natives, to encourage more wildlife and make Christchurch feel like it's in New Zealand and not England. But I digress.
I don't like long words where a shorter word would do. However, "senescence" is a delicious word. It means aging. More precisely, the biological processes of deterioration that go hand-in-hand with age. The leaves of deciduous trees usually turn yellow, red, and brown when they senesce. The green colour in a leaf is caused by chlorophyll, a green protein which helps plants to use the energy from sunlight to convert water and carbon dioxide into sugars. Chlorophyll is contained in structures inside the plant cell, called chloroplasts. The green colour in the leaf fades as chloroplasts degrade, their proteins being reabsorbed into the tree. The degradation of the chloroplasts reveals carotenoids: red, orange, and yellow pigments in the same family as those which turn carrots orange, butter yellow, and flamingos pink. Incidentally, they also indirectly help you see.
So in the leaves of deciduous trees, age and beauty go hand-in-hand. They senesce, turn flame-coloured, and fall to create wonderful thick forest carpets. Here is where my other favourite word comes in: abscission. In botany, abscission is a plant dropping its spent leaves or flowers, or its ripe fruit. When a tree leaf is ready to drop, the tree walls it off with a special layer of cells (the abscission zone) so that there is no longer any nutrient exchange between the leaf and the twig. As the leaf senesces, it produces ethylene gas, which eventually triggers the cells in the abscission zone to digest their cell walls. The cells then go all floppy and start to digest themselves, weakening the point between the leaf and the twig until the leaf finally falls under its own weight.
Ethylene gas is used as a hormone by plants. It essentially triggers aging processes, such as flower opening and fruit ripening (the sweet smell of ripe fruit is due in part to ethylene), as well as abscission. Leaves age and die gracefully, on the plant's terms. The programmed death of leaves in the autumn is part of the life strategy of deciduous trees: senescence begins as the days grow shorter and there's less sunlight to be absorbed by chlorophyll, so there's no point in keeping the leaves alive, and they may as well fall so that their nutrients can be reabsorbed by the tree. Trees use aging to their advantage.
Of course, trees don't make autumn leaves look nice for our benefit, but the serendipitous beauty of autumn leaves is a reminder that there is wonder and goodness in the world, whether intended or not, simply as a byproduct of nature and science.
Autumn is my favourite season. The cooling air brings relief from the inescapable heat of summer. The fire, which has slept since November, can flicker into life again. Apples and pears are available for jam and pie making. Mushrooms spring from the ground after rain. The trees look their best in red and yellow. Autumn is about fruiting and dying; it's a good job that plants die gracefully and quietly, or autumn would be a disturbing season.
Autumn in New Zealand carries a bittersweet note, as most native trees are evergreen. The autumn colours of Christchurch are a testament to how much Europeans have destroyed the native habitat here. I wish the City Council would replace more of the exotic deciduous trees with natives, to encourage more wildlife and make Christchurch feel like it's in New Zealand and not England. But I digress.
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| New Zealand bush in winter. Note the predominant colour. |
So in the leaves of deciduous trees, age and beauty go hand-in-hand. They senesce, turn flame-coloured, and fall to create wonderful thick forest carpets. Here is where my other favourite word comes in: abscission. In botany, abscission is a plant dropping its spent leaves or flowers, or its ripe fruit. When a tree leaf is ready to drop, the tree walls it off with a special layer of cells (the abscission zone) so that there is no longer any nutrient exchange between the leaf and the twig. As the leaf senesces, it produces ethylene gas, which eventually triggers the cells in the abscission zone to digest their cell walls. The cells then go all floppy and start to digest themselves, weakening the point between the leaf and the twig until the leaf finally falls under its own weight.
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| Behold! The stages of senescence and abscission. |
Ethylene gas is used as a hormone by plants. It essentially triggers aging processes, such as flower opening and fruit ripening (the sweet smell of ripe fruit is due in part to ethylene), as well as abscission. Leaves age and die gracefully, on the plant's terms. The programmed death of leaves in the autumn is part of the life strategy of deciduous trees: senescence begins as the days grow shorter and there's less sunlight to be absorbed by chlorophyll, so there's no point in keeping the leaves alive, and they may as well fall so that their nutrients can be reabsorbed by the tree. Trees use aging to their advantage.
Of course, trees don't make autumn leaves look nice for our benefit, but the serendipitous beauty of autumn leaves is a reminder that there is wonder and goodness in the world, whether intended or not, simply as a byproduct of nature and science.
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