In 1854, the essayist Henry David Thoreau published an ode to a morning fire: "Light-winged Smoke, Icarian bird... Lark without song, and messenger of dawn." Scientists, of course, saw the hazing blue of wood smoke - or any smoke derived from burning plant material - as something less poetic. In particular, the smoke from dried leaves of the tobacco plant attracted serious attention from chemists by the end of the 19th century.
Victorian scientists had, for instance, calculated that cigarette smoke was about four percent carbon monoxide, a poisonous gas which directly interferes with the body's ability to absorb oxygen. By the 1930s - as I discovered to my surprise while researching my book, The Poisoner's Handbook - chemists had found a host of other toxic compounds in tobacco smoke, beyond carbon monoxide and nicotine. The list now included cyanide, hydrogen sulfide, formaldehyde, ammonia and pyridine, a component in industrial solvents. So that even 80 years ago, physicians were warning (correctly) that tobacco smoke's chemistry was likely to induce heart disease, high blood pressure, possibly even cancer.
Since then researchers have identified an astonishing 4,000-plus chemical compounds in tobacco smoke. Only a small proportion of these are hazardous, although we've learned from experience, that's more than enough. But what makes that number so interesting is that it tells us - shouts at us, really - that plant smoke is incredibly, amazingly complicated. I mean, why would nature turn a burning leaf into such an explosion of chemical notes and signals?
As it turns out, a paper published this week in the American Chemical Society's Journal of Natural Products offers some real insight into that question. The study by scientists in South Africa and Europe, builds on earlier work showing that some elements in the smoke from forest fires contains materials that literally encourage seeds to propagate, to begin regrowing the forest. In fact. researchers have discovered that by creating "smoke water" - bubbling wood smoke into water - that the result will stimulate many seeds to begin sprouting. Biologists are calling these new bioactive compounds "karrakins", a word so far from the public consciousness that when I input it into Google, the first result is a street address in Western Australia.
Smoke-water may turn out to be a useful growth promoter in agriculture; studies have already shown that it drives some lettuce species into a frenzy of leafiness. But this week's paper adds another layer of complexity. The authors point out that there appear to be compounds in wood smoke that also inhibit plant growth. These inhibitors seem to act as timing devices, telling certain plant species that they should remain hunkered down for now, wait a little longer for the after effects of the fire to settle down.
So that smoke becomes a master regulator, full of secret signals to the plant world around us, telling the tiny hidden seeds when to hide, and when to begin unfurling the first greenery of a recovering forest. We've yet to really decipher that code but it seems to me a gorgeous mystery, as full of poetry as even Thoreau's tribute to the hearthfires of morning.