Under the same natural conditions, the secret of "red face" of a few tree species, such as maple, yellow croaker, torch tree, hawthorn tree and five leaf creeper, lies in that their leaves contain not only chlorophyll, lutein and carotene, but also anthocyanin, a special substance rarely found in other plants. The first reason is that anthocyanins have "anti trend spirit". With the decrease of temperature and the increase of temperature difference between day and night, the content of anthocyanin will not decrease, but will increase rapidly. Secondly, anthocyanin has the characteristics of turning red when encountering acid and "not changing color when encountering alkali". According to the test, only a few plant leaves, such as maple, have acidic cell fluid. Therefore, with the fall of autumn and the increase of anthocyanins, the leaves will gradually turn from green to red. But for most plants, because of the low content of anthocyanin or the high content of anthocyanin, but the cell fluid is alkaline, no matter how the climate changes, the leaves will not turn red.
由此看来,枫叶等少数植物的叶子秋天变红的内因是花青素与酸性细胞液发生化学反应,外因则是入秋后天气转寒,促进了花青素大量增多,即气象条件发生变化造成的。
It seems that the reason for the leaves of a few plants such as maple leaves turning red in autumn is the chemical reaction between anthocyanin and acid cell fluid, and the external reason is that the weather turns cold after autumn, which promotes a large number of anthocyanins, that is, the change of meteorological conditions.
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