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What is "Autumn Leaves"?

Autumn Leaves

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This article was written by Zhou Jianren in October 1946

The name Autumn Leaves is often heard. A few years ago, girls had to have their ears pierced and wear earrings. Under the ring is often hung a small piece of long oval jade with pointed and slightly curved ends and sparse and shallow wavy notches on the edge. This is called an autumn leaf. Sometimes autumn leaves are also embroidered on the embroidery. Foods such as cakes and steamed buns were also shaped into autumn leaves, and this is still done today. Speaking of autumn leaves, the image comes to mind of a kind of leaves that are wider than peach leaves, narrower than plum leaves, and often slightly curved near the front end.

Leaves come in many shapes. The lotus leaf is round and decorated with a rattan sign. The leaves of the palm tree look like folding fans when they first emerge. When they are let go, they crack one by one, like a palm with fingers spread out. The willow leaves are slender, and the buds and leaves are even longer. The sedge grass planted along the steps has ribbon-shaped leaves. What is particularly special is the leaves of onions, which are cylindrical and resemble a tube. But we are not surprised. We know that their ancestors should have had flat leaves, but later, for some unknown reason, they rolled into a round shape and became their current shape. This is our brave inference, but we also make it carefully, because most of the relatives of onions have flat leaves; also, chrysanthemums bloom in autumn, and most of their petals (actually a flower) are flat, but For example, in the "quill" case, the petals of chrysanthemums are rolled into the shape of a tube, which can be used as a circumstantial evidence. It can be seen that flat organs can be rolled into a tube shape. There are also many types of leaves. Why do autumn leaves have a pointed, long oval shape?

Although there are "Mao Ye Dao" and "Onion Tube Candy" in the world, which are all named after the shape of the leaves, there is no doubt that the long oval leaves are the most typical. So, come to think of it, there is no other reason than that this leaf shape is the most common and easiest to recognize.

Winter leaves are available all year round. Short-lived plants, such as chickweed (anciently known as chickweed), are short-lived. The tile grass grows in the ditches on the roof of the house. Buds sprout in spring, then bloom and die when the courgettes are in full bloom. The life of the entire plant is short, and naturally the lifespan of the leaves cannot be long either. Some leaves live for several years, as is the case with leaves of many evergreen plants. Among herbaceous plants, the leaves of orchids and acorus are common examples; among woody plants, the leaves of autumn cypress are also long-lived. But not all the leaves of evergreen plants are like this. The leaves of Osmanthus can only live for one year, but the old and new are connected, and there is no period of bare stems. It looks like it has leaves all year round, and it becomes an evergreen tree. .

Since leaves can be found in all four seasons, why not allow other seasons and add the word "autumn" to call them autumn leaves? I thought: Maybe it’s because autumn leaves are particularly noticeable?

Leaves are generally yellow-green because the cells contain chlorophyll, which is actually contained in a granular prototype plastid. Although chlorophyll is green, it is not a separate substance. It is not just a mixture of chlorophyll A and chlorophyll B. It also contains carotenoid pigments, the main one of which is carotenoids (carrots are rich in this pigment), and Lutein is mixed with carotene in chlorophyll. These mixtures have different strong properties. The chlorophyll is easily destroyed, but the carrot pigments are not. When the leaves are picked, the chlorophyll is soon destroyed and withdraws, but the carrot pigments still exist and turn yellow. Its nature is so tenacious that if the chicken eats it, it will always be stained in the egg yolk. If the chicken does not eat things containing this pigment, the egg yolk will not be yellow. The Russian plant physiologist Timiliazov was the first person to separate this yellow substance from chlorophyll.

It seems that in the autumn, the chlorophyll of plants is destroyed. Because the weather is cold, new chlorophyll cannot be produced to replenish it, but the yellow pigment is not destroyed and remains, and the leaves turn yellow. This is easy to understand.

But the leaves in autumn do not just turn yellow. Some turn bright yellow, some turn red or red, and some are brown. For example, maple leaves and birch leaves turn red or yellow. , trees and beech trees will turn brown, giving the leaves a beautiful autumn color. I think that the special name of Autumn Leaves probably has something to do with it, although the Autumn Leaves of the earrings are green (made of jade), the Autumn Leaves Steamed Buns are still white.

Why do leaves turn such colors in autumn? Mainly, a substance called anthocyanin is produced in the leaves.

This substance is often found in flowers. It turns bright red when exposed to acid and blue when exposed to alkali. Sometimes mixed with other colors, showing different leaf colors. Because anthocyanins will change color when exposed to acid or alkalinity, some flowers will change color because of changes in the cell fluid. Such anthocyanins are also produced in red leaves in autumn, but the formation of this leaf color requires sugar and sunlight. Only sunlight can produce sugar, and sugar can produce anthocyanins. So it appears full red, or purplish. Colors such as maple leaves are very beautiful. Ordinary brown is produced by the cell walls of leaves containing a lot of tannins. Bright yellow also requires abundant sugar to be produced. The production of sugar is related to sunlight. As early as 1874, the botanist Bataline published an article saying that there is a kind of flat phase. In cold weather, the branches exposed to the sun turn golden yellow, while those in the shade remain green.

Because the production of anthocyanins requires abundant sugar, according to botanical observers: If the weather is sunny and frost suddenly occurs in autumn and winter, you can see brighter and more beautiful autumn colors. Because sunlight causes more sugar to be produced in the leaves, the weather suddenly becomes colder, destroying chlorophyll and blocking the consumption of sugar, thus producing delicious autumn colors in gloomy and mild weather. However, the yellow color of many leaves is only due to the destruction of chlorophyll, leaving only the long-lasting carotenoid pigments, as mentioned before.

The leaves in autumn are indeed very touching. Although the fallen leaves fluttering in the autumn wind can also attract people's attention, the most eye-catching thing is the red leaves in autumn. I remember reading a short story written by Ms. Caggins in a psychology book. It said that a man once went to bed early and did not wake up. The sun shone in and shone on his eyelids, and he dreamed of walking on the mountain and seeing red leaves. It is true that many simple dreams are clearly caused by hazy perceptions, which are commonly called sensations in ordinary books-or certain stimuli. Once upon a time, a Frenchman experimented with dreams and asked a servant to sprinkle water on his forehead while he was sleeping to see how he was doing. He then dreamed of traveling in the tropics and sweated on his forehead. Not all natural dreams are so simple, and this question is too far away from the topic, so I won’t talk about it here.

If you feel strange seeing the beautiful autumn leaves, why do they turn into this color? Then, as long as we know that the petals are originally changed from leaves (in fact, even the male and female, not to mention the calyx), it will not be strange at all. The German poet Goethe discovered this very early. After the leaves change into petals, they can show various colors. But leaves are still leaves, and they can only appear in several colors such as red, yellow, red-purple, brown, etc. in autumn.