I live in the northeastern United States, so this time of year I
think about leaves a lot. The color changes are the most obvious
reason to be thinking about leaves, of course. In the autumn,
the trees slow down and then stop producing chlorophyll, the
green pigment needed for photosynthesis, so the yellow pigments
also in the leaf become more prominent. But it’s probably more
complicated (and more interesting) than that: yellow leaves are
a sign of disease during most of the year, so some insects are
attracted to plants with yellow leaves. If a tree is already
ill, it might be more vulnerable as insect food. It appears that
some trees actually produce red pigments to hide the yellow
pigments since the green pigments are no longer doing so, and
it’s all to protect themselves from insects. And it’s probably
really even more complicated than that, too. (I love science:
it’s always more complicated, and we’re always wrong, but it’s
so much fun to try to figure it out.) So there’s one thing to
think about when wo