Dear Cecil:I'm sure I remember hearing from a reliable source, i.e., a science program, that certain species of trees (or shrubs) will spontaneously combust in order to ensure the survival of the species. I'm being mercilessly teased about this, so I'd appreciate any information you can dig up. --Donna Rose, Washington, D.C. Cecil replies:
No offense, Donna, but this is a pretty dull way of putting it. A more interesting way is: Could the biblical burning bush that spoke to Moses have been a spontaneously combusting desert shrub? Answer: Maybe. Some claim there's a plant in desert regions that every so often bursts into flame for no apparent reason. And here your idea of plant-based excitement was watching the leaves turn colors. Then again, I suppose if you were a desert home owner observing the spectacle of random ignition on the lawn some night, you might also think: Cheezit, couldn't I just have crabgrass?
But first the question you asked, as opposed to the one I feel like answering. The science program you heard likely was speaking of pyrophytes, plants that have adapted to fire in various ways. The cones of several species of pine, for example, are serotinous--that is, they open only when exposed to extremely high temperature, making fire an essential part of the reproductive process. (Bruce Springsteen once wrote a song about this.) The fire has to be of external origin, though--the pines don't torch themselves.
It's possible some other plants eliminate the middleman. The leading candidate is Dictamnus albus, a flowering shrub that grows to a height of about two feet. Native to a wide swath of Europe and Asia, including Israel, it's commonly called "fraxinella," "dittany," and, more pertinently for our story, "gas plant" and "burning bush." On warm days D. albus exudes vapor that readily ignites if you hold a match to it, and some say it ignites all by itself if the sun is hot enough. But--here's where things start to get biblical--the vapor burns so quickly that it doesn't consume or even damage the plant. This naturally brings to mind Exodus 3:2: "And the angel of the Lord appeared unto [Moses] in a flame of fire out of the midst of a bush: and he looked, and, behold, the bush burned with fire, and the bush was not consumed."
So D. albus is Moses's burning bush, right? Many biblical commentators think so (or at least they think the bush was a spontaneously combusting plant). But I'm not staking my King James on it. Straight Dope research assistant Bibliophage has turned up an apparent case of spontaneous combustion involving a cactus (www.ananova.com/news/story/sm_567529.html), but nobody in a position to speak authoritatively, e.g., a botanist in Israel, could confirm that such things happen on a regular basis. What's more, the seemingly miraculous biblical story is put in a somewhat Martha Stewart-ish light if we assume burning ornamentals are a commonplace feature of Mount Sinai life: "And behold, the angel of the Lord spoke unto Moses from a lovely spread of flaming fraxinella." All of which means we'd be jumping the gun to conclude that Dictamnus albus, or any other plant, spontaneously combusts in order to perpetuate the species.