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  • Paul Anthony Jones


(n.) the growth response an organism makes when it encounters an obstacle

aphercotropism in action as tree roots follow the cracks in a pavement

Well, well, well. Every so often something just seems to click over on @HaggardHawks, and one unsuspecting tweet suddenly goes a bit berserk. The goldfinch did. Tantling did. The racehorse with the best name in history did. And that fantastically wind-sculpted tree undoubtedly did too.

But earlier this week, an obscure nineteenth century ecological term (paired with a tremendous photograph, for which we can take no credit whatsoever) broke all the HH records:

Understandably, the obscurity of a word that seems seldom (if ever) to be used outside of old scientific literature—and so isn’t found in the pages of any major dictionaries—raised a few eyebrows:

So, 800 retweets and nearly 1000 favourites later, we thought you might like to know a bit more about aphercotropism, and thereby address a few of these queries (and the dozens more like them). Scalpels at the ready, then—let’s dissect this thing.

First of all, the prefix ap– or aph derives from a Greek word, apo, meaning “off” or “away from”. It’s the same root we see in words like apocalypse (which literally means “uncovered” or “disclosed”), apocryphal (literally “hidden away”), and even apology, which originally referred to a formal defence or justification, or to a personal account of a story (and so literally means “from speech”).

Secondly, the –erco– part comes from another Greek word, herkos, referring to a fence, a barrier, or a some kind surrounding wall. It only has a handful of offspring in modern English, the majority of which are fairly obscure, long-forgotten terms (the kind that HH devours) that have found their way into the dustier corners of the OED: hercotectonic (“pertaining to the construction of walls”), poliorcetic (“relating to the besieging of cities”), and hercogamous, a botanical term describing plants that grow “barriers” between their male and female parts in order to prevent self-fertilization. Apparently.

So that only leaves the suffix –tropism, which you’ll likely recognise from words like heliotropism (“turning towards the sun”) and phototropism (“growth towards a light source”). Scientists and ecologists have invented dozens of words for different kinds of “tropism” besides these, of course, including geotropism (“growth dictated by gravity”), thigmotropism (“movement in response to touch”), homolotropism (“fixed horizontal growth”), and thixotropism, which refers to the property of certain fluids that makes them act like a solid when subjected to a force—which is why you can run across a pool of custard.

Wait a second—let me just stop to add those last six words to my bucket list… Right, let’s carry on.

Tropism derives from another Greek root, tropos, which literally means “a turning”. So when we put everything back together, aphercotropism ultimately refers to an organism quite literally “turning away from an obstruction”. That’s all well and good, of course, but it still doesn’t explain where the word itself comes from. Did we just make it up?

No. Seriously, no. Believe me, finding out about genuinely interesting genuine words is much more fun than making them up. Instead, this particular term seems to date back to the late nineteenth century, with the earliest record we’ve so far uncovered coming from an 1899 volume of Nature Notes, a natural history journal published by The Selborne Society, an early conservationist organization:

Aphercotropism … is a peculiarity discovered by Darwin. His experiment was as follows: after allowing a radicle to be well developed in peas, beans, &c. the seed is suspended in the air. A tiny piece of card is attached to one side of the tip by a little gum; the tip will now move away from the vertical position, on the opposite side to the card. The tip may make one or more complete circles in a vertical plane; and it has been known to pass through the first loop so as to tie itself into a knot. This explains how a radish was once dug up and found to be thus tied up.

Charles Darwin outlined this experiment—in which the root of a single pea plant grows in an obscure shape in order to avoid the card glued above it—in his 1880 work, The Power of Movement in Plants. But in his account, he makes no reference to the word aphercotropism. So until any other evidence comes to light, we can presume that the word was coined sometime between the publication of Darwin’s book in 1880, and the publication of the Nature Notes journal in 1899, the author of which likewise makes no reference to having coined the word himself. Precisely who did coin the word, ultimately, remains a mystery.

Right. Now, back to that custard thing…

Grateful thanks to avid HH-er John (no surname supplied, unfortunately!) who emailed to say—quite rightly—that the second Greek root of aphercotropism is ‘herkos’, not ‘erkos’ as this blog previously stated. For those of you not up to speed with your Ancient Greek (a minority, surely...) this is to do with rough breathing, an Ancient Greek diacritic marker that indicated a vowel was preceded by a “h” sound; this should be transliterated into English with an initial H, which we had omitted. The post has now been updated accordingly. Apologies for the oversight—a more up to date dictionary of Ancient Greek has been purchased here at HHHQ. The other has been unceremoniously banished to the back of the cupboard.

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