They All Fall Down

It's started! They come quietly, one by one, then in bigger numbers and before you know it the invasion has begun. Leaves, in their millions, have started to decend on Worcester College, but the gardening team will not be defeated. Armed with rakes and leaf blowers, they battle to stem the attack. It is about equal at the moment, but as this September has been the driest in 12 years, the leaf fall is speeding up. The big leaf collecting machinery will be brought in to play soon and the gardening team will unite, all for one and one for all.

Now for the educational part of this blog entry, Why do the leaves fall?
The beginning of leaf drop starts when an abscission layer is formed between the leaf petiole, the small stalk attaching leaf blade to the stem, and the stem. This layer is formed in the spring during active new growth of the leaf, it consists of layers of cells that can separate from each other. The cells are sensitive to a plant hormone called Auxin that is produced at a rate consistent with that of the auxin from the body of the plant, the cells of the abscission layer remain connected; in the fall or when under stress the auxin flow from the leaf decreases or stops triggering cellular elongation within the abscission layer. The elongation of these cells break the connection between the different cell layers, allowing the leaf to break away from the plant, it also forms a layer that seals the break so the plant does not lose sap.