Tuesday, October 09, 2007
I was taught (perhaps as late as high school?) that color developed in leaves as the chlorophyll died back, allowing other colors to be seen.
I just finished "The Velocity of Honey", an interesting book of essays on science by Jay Ingram. Jay apparently likes to investigate questions that appeal to him and then write about them. How nice that so many of his questions appeal to me as well.
One essay in this book deals with the subject of fall color - particularly reds. Apparently research done in the '90s (long after my time) has determined that reds are not simply present in the leaves and only visible when the green is gone. instead, the reds (anthocyanins) are actively built by the leaves as the chorophyll is being dismantled and stored away in the roots. The reds are sunblock! The purpose of building these anthocyanins appears to be as protection against sunlight ruining the chlorophyll while it is being taken apart and very sensitive to excess light. Consequently, the reds appear first in leaves that are exposed to more light than others, such as on ends of branches protruding from the bulk of the tree on southerly exposures. That describes this tree's turned leaves exactly.
It also explains why there is little color in years when fall is wet (a phenomenon referred to in my family as "raining the leaves off the trees"). If it's cloudy over, no sun block is needed, just as my kids keep complaining to me when I run after them with sun block on grey days in the summer.