The reason why some maple leaves do not turn red in late autumn is that if the temperature drops slowly, the temperature difference between day and night is small, the chlorophyll has not been destroyed and the trees have withered, then the leaves are green, even with yellow spots. Maple leaf, maple leaf is the leaf of maple tree, and also an important symbol of Canada. Maple leaves are generally palmately pentalobed, 13 cm long, slightly wider than long. The three largest lobes have a few prominent teeth, the base is heart-shaped, the leaf surface is rough, the upper part is medium green to dark green, the lower vein axils have hair, and it turns yellow to orange or red in autumn. However, a few areas are dark and dark green. Maple leaf is a spiritual symbol in people's mind. Because of its particularity, people often use it to symbolize perseverance. Autumn is the best season to watch maple leaves. With the gradual decrease of chlorophyll content, the colors of other pigments will gradually appear on the leaves, so the leaves will show yellow, red and other colors. The external factor for the discoloration of maple leaves is the climatic conditions: when the temperature rapidly drops to a certain extent, and the temperature at night is much lower than that in the day, the leaves have not yet withered, and most of the chlorophyll has been destroyed. At the same time, the increase in the temperature difference between day and night is also conducive to the formation of anthocyanins, so the leaves turn red quickly.