From Falling Leaves to Black Holes Gravity Works in Wondrous Ways
A thin layer of cells at the base of each leaf stem literally cuts the leaf off from the tree. Gravity assists in the process. Bob King I've spent a lot of time in the forest lately watching leaves fall. When the wind blows they spiral, seesaw, twirl and drop to the ground. Leaves also fall when there's no wind. On an utterly still day this September I listened to the scratch and clatter as one leaf here and one leaf there broke free and tumbled earthward, guided by gravity. We know that leaves change color because the chlorophyll that drives photosynthesis breaks down and exposes other pigments that have been there all along. But why exactly do leaves fall? It turns out that trees simply get rid of them. They're baggage that might otherwise drain resources from the plant when the weather turns cold. In response to a decrease in sunlight a tree makes special abscission cells that form along the juncture of the leaf stem and branch and slowly push the leaf away, cell ...