I have an article in tomorrow's New York Times about the mystery of autumn leaves. Insect warning? Sunscreen? The debate rages. The one thing I was sad to see get cut for space was the statement by one of the scientists that the answer might be "all of the above." This sort of multitasking is the cool--and sometimes maddening--thing about living things. Very important, and very hard to sort out.
More like this
When we look at a the data for a population+ often the first thing we do
is look at the mean. But even if we know that the distribution
I love this question:
Why is it warmer in the summer than in the winter (for the Northern hemisphere)?
Go ahead and ask your friends. I suppose they will give one of the following likely answers:
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Last week we looked at the organ systems involved in regulation and control of body functions: the nervous, sensory, endocrine and circadian systems. This week, we will cover the organ systems that are regulated and controlled.
I had always noticed that if a healthy tree limb is cut off with healthy leaves, the leaves will not go through the usual autumn color transitions. Instead the leaves brown and wither away, calling into question, as your elucidating article does, the commonly held notion of the fall "dying leaves." I have also noticed that the dead leaves from a severed tree limb will often remain firmly attached to the tree limb for a considerable amount of time longer than their autumn counterparts. Perhaps the trees have also evolved an adaptation for dislodging the leaves from the limbs in the autumn to allow new growth in the spring?
The trees use abscisic acid to dislodge the leaves.
Best,
D
Jed: Leaf abscission is an active cellular process--on a severed branch the process does not happen and the leaves won't fall off in the normal, living way. If you mutate certain proteins involved in abscission, the leaves won't fall off at all; if you sever the branch it follows that the abscission process is aborted. The breakdown of chlorophyll is also an active process involving many cellular proteins and trafficking pathways.