Wednesday, September 21, 2011

Changing Leaves: Science or Philosophy?

Entertaining TV for nerds and people who like explosions.
I don’t have a very scientific mind.  That’s not to say that I don’t occasionally watch Myth Busters or that I don’t want to know why things are the way they are – I just mean that when it comes to complex science my brain takes a little while longer to process things if I can process them at all. 

One of the primary reasons I bother with learning the science of things though is so that I might later be able to tell someone that they are wrong.  Petty, I know.

While following links today, I was led to the web site of a professor of plant physiology at Appalachian State University.  He calls himself “The Fall Color Guy.”  That sounded like a good place for scientific simpleton's like me to find a few takeaway factoids that could prove useful to me later on.  

My step father is of the age where he has a few pet shticks.  One of them is a conspiracy theory related to Daylight Savings Time.  Another one is that he has always claimed that leaves change colors in the fall because of the changing trajectory of the sun’s light waves.  That’s the kind of thing that sounds just scientific enough that it could be true but it also sounds like total bull to me because I am pretty sure it has something to do with chlorophyll and not light.  But I never challenged him on it because I didn't know the real, complete answer.  I have operated on the assumption that it had something to do with the colder temperatures causing chlorophyll to recede from leaves but I had no idea if that was totally correct and I had no explanation for why the colder weather would cause that effect.          

This is what passes for fall "color" in my neighborhood.

So, having stumbled upon a site written by the Fall Color Guy, I decided it was high time I got an actual, reliable scientific explanation for what causes the color of leaves to change in the fall even if it meant I would have to turn on, warm up, and then actually use the left side of my brain to decipher the explanation.

I clicked around the web site trying to find a one-sentence answer along the lines of “because it gets cold and trees stop making chlorophyll in the cold” when I stumbled upon the following paragraph:

“Why do leaves appear Green?  [emphasis added]  The green color in leaves results from the production of a compound called chlorophyll (chl). We see the leaf as green because this compound is most efficient in absorbing red and blue wavelengths of light, and relatively inefficient in absorbing the green wavelengths. This means that the light reflected from the leaf back to our eyes is enriched in the green spectrum, making it appear green to us.”

I’ve been thinking about this for a couple hours now.  It is, quite frankly, blowing my mind.  This isn’t just science we're talking about, its philosophy.  Its metaphysics! 

Aristotle - the "father of metaphysics".  I wish I could ask him about how we know what colors we are really seeing.
Given that he has apparently lost all his color, I think he'd have something important to say about the subject.

If the leaf just appears to be green then that statement implies that the leaf isn't really green.  And if it isn't really green then couldn't it be said that green leaves don’t really change colors in the fall since they weren't green in the first place?  Do leaves merely appear to change colors in the fall?  Or, more accurately, do we just start seeing leaves as they really are when fall comes?  If that’s the case, then what sounded like an absurd supposition made by my step father could actually have some truth to it.  After all, if the chlorophyll does a bad job at absorbing green wavelengths, could the different trajectory of light waves in the autumn reduce the amount of green wavelengths reflecting off leaves? 

Clearly, I still had too many questions to let it rest at this so more reading was required. 

A Japanese maple photographed in November of 2010 with what "appears" to be fall colors.

A few clicked links later and I was on the USDA Forest Service's web site which had a page titled "Why Leaves Change Color."  It still didn't provide me with a sound byte answer, but this was close:
"During the growing season, chlorophyll is continually being produced and broken down and leaves appear green. [There's that word "appear" again!]  As night length increases in the autumn, chlorophyll production slows down and then stops and eventually all the chlorophyll is destroyed.  The carotenoids and anthocyanins that are present in the leaf are then unmasked and show their colors."
Okay, I accept that it's a scientific process that causes leaves to appear to change colors in the autumn.  But I prefer my philosophical interpretation of the annual occurrence: leaves only reveal their true identities in the fall.  In my half-working mind, the changing colors of leaves encourages me to remember that what I see on the surface isn't always a true reflection of the essence of a thing.  I suppose that's true for people too. 


The USDA's web site had some other good explanations for what triggers the changes in color, what leaf fall does to the tree, and what role weather plays in it all, but frankly, I OD'd on science for today and I'll just have to bookmark the site for future reference.  Hopefully I'll get back around to it before my mom and her husband come to visit again. 


  1. It's interesting that some plants change colors, yet others don't. Love the interesting changes though.
    Cher Sunray Gardens

  2. The science of color perception is complicated. My science-oriented brain sees the changing of fall leaves more as a blend of physiology, and physics, than metaphysics. Fortunately we have those wonderful tiny color receptors in our retinas, called cones, that enable us to see these differences in wavelenghts of light...just imagine how dull the world, and fall leaves, would look without them!

  3. If a tree falls in the forest and no one is around to see it, does it still "appear" green?

  4. I concur with Curbstone. All science all the way. The kink in the plan here is color blindness. Just ask a color blinded person how they perceive and you answer is different. Still the same physiology and science, but different. Questioning if green really 'exists' is awfully deep thinking though.

  5. Who knew so many of you would be science-oriented? I certainly didn't, but I'm glad to read it. I am really interested in the whole concept of color perception now. And I can see how color blindness complicates the issue . . . but is color blindness a physiological problem with the affected person's eyes rather than an argument against the laws (if they are "laws")regarding color perception?

  6. Chad, my husband is color-blind, but now who's to say just because he has difficulty telling green from brown and certain reds from purple that he's wrong? Maybe he's seeing things the way they really 'are' and not the way they 'appear' to be. This is frankly rather unsettling to me, since I always thought I had the upper hand when it came to Name That Color. Now I'll have to eat my words when he finds out it is a possibility that green doesn't really exist. Drat.

  7. This is something you could think about for hours - no days, or weeks, or like the Fall Color Guy - a lifetime. I always wonder how the animals see things. We see green - but who really knows what color things are? Some animals may see red there instead. Who's to say what's really right? It is also interesting to think that the fall colors are the "true" colors, and that the green we love so much is just a coat they put on to protect them from the sun.

  8. So leaves show their true colors in Fall...interesting :)

  9. "One of the primary reasons I bother with learning the science of things though is so that I might later be able to tell someone that they are wrong. Petty, I know."

    You've just described my entire existance. Do you think I studied my arse off in school for my Forensic Anthropology degree to actually WORK in that field?

    No! I got it so I could gripe and complain about all of the things they do wrong on 'CSI'. It's totally worth it.

    Anyway, you didn't just blow your own mind with this post, you blew mine too. I think my brains have started leaking out my ears...

    Which is a good thing! That was an awesome post. Much more educatonal than my usual written fare on penises and weird customers.

    I love fall, it's my favourite season. I like the pretty colours and not sweating my balls off.

    Can I say 'balls' on your blog? Since your mom isn't reading, I figured it would be ok.

  10. Chad, I've been thinking about color perception recently, too, so I found this post (and the comments) especially interested. What triggered my musings was not fall foliage but the fact that many of the blue flowers in my garden appear more intensely blue on cool, crisp mornings. Is it that they really are a more intense blue, or is it just that the dry air changes my perception of the light waves? (I'm pretty sure the Blue Paradise phlox, which can go from electric blue in the morning to hot pink in the heat of a sunny afternoon, really changes color.) -Jean

  11. Catching up on my reading, and found this article, that totally made my day! Psychologists believe that color does not really exist at all, but is related to the anatomy of the eye. Dogs don't see color. Merely a physiological phenomenon.