If you’re like me you have to know how everything works. To be honest, I don’t understand how some people stumble through life without understanding how everything works. Take Fall colors for example. In many regions the trees change every year yet most people are completely ignorant of the chemical mechanism by which this occurs.

Basically, tree leaves have several color pigments. Most of the time we only see the one present in the greatest quantity, chlorophyll (the green one, duh.) However, in the autumn the trees somehow “know” that winter is coming and it’s time to drop the leaves before they all freeze and become useless anyway. The mechanism by which this occurs actually depends on the length of the nights; not the length of the days as many people believe. In the leaves there’s a chemical that mediates the “color change” response by governing the rate at which chlorophyll is replaced in the cells. This chemical actually degrades in the dark. Therefore as the nights get longer and longer the level of the chemical in the leaves eventually reaches a lower threshold triggering the leaves to replace less and less of the chlorophyll. As this happens you see less of the green and more of the other colors that have always been there but haven’t really been visible.

Temperature and daylight conditions also mediate this response, as the physiological response within the leaf is affected by things like cloudy days, warm nights. A cloudy, warm fall produces drab colors, probably because the leaf doesn’t have to produce as many non-green pigments to maximize its nutrient production before winter sets in.

After reading up on this subject to refresh my memory, I get the impression that this subject is still not well understood. I still see articles that say the color response is mediated by light exposure, which is actually half right. As far as I’m concerned, half right is equal to totally wrong when it comes to science.