The Lime tree (Tilia Cordata, or the Linden tree) is found all around Oxford. As I cycle under the avenue of them on South Parks Road I can feel the slight prickle of honeydew falling.
Honeydew is a sugar-water liquid secreted by the aphids who live on the Lime trees. They suck the sap and excrete the liquid which falls in a light spray from the trees. The leaves quickly get a shine where large amounts of this liquid has dried on them. I've seen this in other places around Oxford.