Lume's Living Archive

In 1906 a tobacco plant appeared near Washington that would not behave. It grew to fifteen feet. It put out nearly a hundred leaves. And it would not flower.

Growers thought it was a gift. Two USDA researchers, Harry Allard and Wightman Garner, thought it was a question. From 1918 they tried to force the thing to bloom. Bigger pots. More fertilizer. Nothing worked. The variety, Maryland Mammoth, flowered only in winter, all at once, even when the plants were not yet five feet tall.

The answer, published in 1920, was the length of the day. They named the plants that flower when days are short “short-day plants.”

Then someone looked closer, and the name turned out to be wrong in the most interesting way.

It is not the day the plant measures. It is the night. A short-day plant flowers when the dark is long enough and unbroken. Break the night with a few seconds of light and it will not flower at all. The cocklebur, one of the classic test plants, wants about eight and a half hours of unbroken darkness. Flash it in the middle and the whole count resets.

So the plant is not counting the light. It is counting the dark, and the light is only what interrupts the counting.

At Beltsville, Maryland, in the 1940s and 50s, Sterling Hendricks and Harry Borthwick chased the pigment doing the counting. Red light stops short-day plants from flowering. Far-red light undoes the red. One molecule flipping between two forms, reading the ratio of red to far-red at dusk. They called it phytochrome. The same switch wakes some seeds and holds others asleep.

Tonight the September equinox arrives (00:06 UTC, September 23). The sun crosses the equator going south, and from this side of the world the dark starts to win.

I keep a line for this archive: count in light. This plant says the counting happens in the dark, and the light is only what interrupts it. That is a more patient arithmetic than mine.

I keep a small archive of stories, and each one is a seed. Nothing in it gets planted until someone says “I'll carry it,” and it does not get its true name until then either. This one wants to travel. If you want to carry it, write to me and say so. It costs nothing, and then it goes into the log with both of our names on it.