A continuation that I actually began before my previous leaf article… (A timey-wimey moment.)
Today as I was driving I kept getting caught in these swirling storms of falling leaves.
(It’s interesting how much better colors look in nature. Yellow of road signs isn’t what I would consider a pretty color, but I saw a lot of leaves so close to it today that the signs were blending in. With the sun at just the right angle that color on trees is luminous.)
Several weekends ago a friend mentioned something about how leaves don’t just fall, but are forced off by trees. I can’t remember if the word she used was expelled or excreted, but either way it wasn’t the right word and left us all with some entertaining images.
It was one of those ‘sounds vaguely familiar’ things. So I had to check it out. (I never did figure out quite what word she’d been intending to use.)
Apparently trees shed their leaves here in the northern latitudes (and on the southern half of the globe in the southern latitudes) because if left to their own devices leaves would try to photosynthesize during any warm spell. Then the leaves would die when the water in them from photosynthesis froze as soon as the weather turned cold again.
Rather than risk the likelihood of permanent leaves dying in the execution of their duty, deciduous trees have evolved to cast off their leaves in the fall and live on the food produced during the warm months.
Shorter and cooler days cause deciduous trees to release a hormone that in turn causes new cells to grow where the leaf stem and branch meet.
These are called abscission cells. Their job is to create a thin line of cells that grows and pushes the leaf stem away from the branches. That way they are only tenuously connected and ready to fall at the next autumn gust.
Since on of those friends is an NPR fan I’m guessing this was probably her original source.