Plant Cuttings

Suck on this: predictions and patience in phytobiology

Image: Thomas William Wood, in ‘Creation by Law’ by Alfred Russel Wallace, The Quarterly Journal of Science vol. 4, 1867.
Image: Thomas William Wood, in ‘Creation by Law’ by Alfred Russel Wallace, The Quarterly Journal of Science vol. 4, 1867.

One of the great strengths of the scientific method is its ability to make predictions that can be tested. One of the most famous of those predictions is Charles Darwin’s oft-cited 1862 inference that a long-throated flower (‘with a nectary a foot long’ – approx. 30 cm for non-Imperial readers) from Madagascar (Angraecum sesquipedale or Darwin’s orchid) would be pollinated by an equally long-tongued insect. Despite being a pronouncement by the venerable naturalist – or maybe because of that? – the assertion was controversial at the time and not without its detractors. Nevertheless, this incident helped to place the notion of insect–plant co-evolution firmly onto the agenda and started a debate that continues into the 21st century (e.g. Miguel Rodríguez-Gironés and Ana Llandres). Sadly, the Great Man never lived to see his prediction confirmed and his prescience vindicated – that only happened in the late 20th century, but a fitting tribute to this remarkable story has been produced by Joe Arditti and colleagues. For many years the identity of the nectar-sucking moth was not known. Although the appropriately named Xanthopan morganii ssp. praedicta (Morgan’s sphinx) was mooted as the likely pollinator, this was not conclusively demonstrated until 1992. It is a fascinating tale that is richly illustrated – both with images and quotes from the correspondence that passed between the major players in this saga – and is a nice bringing together of plants, people and personalities (including the ever-interesting if much over-shadowed Alfred Russel Wallace). But those beneficial long tongues come with costs, as Brendan Borrell has demonstrated for orchid bees, not least of which is the need for their owners to have a firm grasp of the physics of fluid flow! Closer to home, long tongues amongst humans are rare enough to be considered an ‘abnormality’ and ownership thereof may incur serious ‘lost opportunity’ costs as one hyperglossic boy discovered when he lost his place at a school in Malavalli (in the Mandya district of India) as a result. [For the record – maybe literally – the mean tongue (technically, a proboscis) length of the hawkmoth is a staggering 22 cm; the mean spur length of the flower is 33 cm – Ed.]

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