Why Leaves Really Fall Off Trees

Why do leaves really fall off trees? It's not the wind. It's not the cold. It's because trees use 'scissors' to cut their leaves off. Around this time of year in the Northern Hemisphere, as the days grow shorter and colder, those changes trigger a hormone in leaf-dropping trees that sends a chemical message to every leaf that says, in essence, 'Time to go! Let's part company!'

Once the message is received, little cells appear at the place where the leaf stem meets the branch. They are called 'abscission' cells. They have the same root as the word scissors, meaning they are designed, like scissors, to make a cut.