Because of a summer of rain, the trees up north where I have been for the last few weeks are only now beginning to turn. Some years ago, as an innocent, I shared a car ride with a Professor of Botany and two Professors of Forestry, as we went to a wilderness retreat. At one point, as we were proceeding through a wood that was a multicoloured spectacle, I turned to my eminent colleagues and said, "So why do the leaves change colour?" That was the last moment of peace for the rest of our journey. Each of these eminent figures had a different theory, which they held to with vicious belief. Voices were raised; cutting words were spoken. Over the ensuing weekend, the three professors hardly spoke to each other, and I am reliably informed that, while they were never exactly friends before, they have been bitter enemies ever since. The cheering part of this for me is that I have never felt as intimidated by experts since; the depressing part is that I still don't know why the leaves change colour.