Most of the fallen leaves of plants are with their backs facing upwards and their leaves facing downwards. This is not a trick played by the autumn wind, but the special structure inside the leaves.

Most plants have leaves, leaf backs and leaves.

There is a significant difference in sunshine during the growth process, which leads to different structures on both sides of the leaf: the cells near the leaf surface are usually rectangular and arranged regularly, which is called palisade tissue; Cells near the back of leaves are irregular blocks called spongy tissues. The palisade tissue is closely arranged and contains a lot of chlorophyll, which is mainly used to receive light energy, and uses carbon dioxide in the air to produce a lot of organic matter with high density; Sponge tissue is loosely arranged with less chlorophyll. Mainly used to store products and water in plants, with low density. Therefore, not only the color of the leaf surface is usually brighter than that of the back of the leaf, but also its weight is relatively large. When the leaves fall from the tree, the heavier leaves will face down and the back of the leaves will face up. (Liu Yudong)