Chlorophyll

The word was coined in 1817 by two French chemists, Joseph Bienaimé Caventou and Pierre Joseph Pelletier, who extracted the green pigment from leaves and gave it a name built from two Greek roots: khloros, meaning "green" or "pale green," and phyllon, meaning "leaf." The name is elegantly literal — green-leaf — and the two men chose Greek in the established scientific tradition of conferring classical dignity on new discoveries. They were working in the same productive years that gave science caffeine, quinine, and strychnine, all extracted and named by similar chemical means.

What Caventou and Pelletier had isolated was the pigment that makes photosynthesis possible — the molecule that sits inside chloroplasts and absorbs sunlight to drive the conversion of carbon dioxide and water into sugar and oxygen. Chlorophyll's peculiar achievement is its selectivity: it is poor at absorbing green light, which is why it reflects green back to our eyes. The molecule evolved not to appear green but to harvest the energetically useful wavelengths that flank it, and green is what is left over, the unwanted portion returned to the world as color.

The khloros root that enters chlorophyll has a rich linguistic history in Greek. Homer used it to describe the pale green of young plants and, strangely, of honey. The word also gave English "chlorine," named for its pale green-yellow color when gaseous, and "chlorosis," the condition in which plants lose their green due to iron deficiency — a sickly yellowing that gardeners recognize as a sign of soil too alkaline for iron uptake. All these words share the original Greek sense of a particular, slightly uncanny green.

In the autumn, the story of chlorophyll becomes a story of unmasking. As days shorten and temperatures drop, deciduous trees stop producing chlorophyll. As the green pigment breaks down and is reabsorbed into the tree for storage, it reveals the yellow and orange carotenoid pigments that were always present in the leaf, hidden beneath the chlorophyll's green. The reds of autumn are different — anthocyanins produced fresh in response to bright light and cold — but the yellows were always there, waiting for the chlorophyll to step aside.