This picture depicts a landscape painted from a position within a few metres of that used by John Constable for his painting Flatford Mill, now in Tate Britain (see “Fieldwork at Flatford”). It shows part of the same scene almost exactly 200 years after he painted his picture, albeit at a somewhat larger scale (the leaves in the background are only a few millimetres long). It is based upon the handful of pondweed that I pulled out of the River Stour on 30 December, and the algae that are associated with it. In the foreground, there is a filament of a green alga that we have not named to our complete satisfaction, but which is either an unbranched Cladophora or Chaetomorpha e linum. Also present in the foreground is a chain of the diatom Ellerbeckia arenaria (see “Ellerbeck and Ellerbeckia”) and, at top left and bottom right there are chains of Melosira varians. The pondweed leaves are smothered with Cocconeis placentula cells and, at the top right there is a cell of Gyrosigma attenuatum gliding across the pondweed leaf. Proportions are roughly in line with what I saw down my microscope and the cells of Melosira are approximately 20 micrometres (1/50th of a millimetre) in diameter.
Constable never saw this particular scene on the River Stour partly because he was not (as far as we know) a microscopist, but also because Elodea canadensis, whose leaves that create the backdrop for the image, was not introduced to the UK until after he died. The river would have been different in other ways, too: lower concentrations of nutrients and agrochemicals, in particular. There would have been different submerged plants, but maybe some of the algae growing on their leaves would have been different too? I was involved in a study a few years ago that looked at this question, using aquatic plant specimens from herbaria. None dated back as far as Constable, but we did see some significant shifts in composition of the attached algae in samples from 100 years ago, compared with now.
The Greek philosopher Heraclitus once said: “no man ever steps in the same river twice, for it’s not the same river and he’s not the same man.” Perhaps we can also say that no-one looks at the same landscape twice, for it, too, is always changing. There is a paradox here, because landscape has, at its core, a geological form that change infinitesimally slowly whilst at the same time being cloaked in an ever-changing raiment of vegetation. Rivers are a curious mix of a fixed landscape feature and, as recent floods have reminded us, highly dynamic systems. And landscape is also a matter of scale: Constable lifted his eyes to the horizon and showed a naturalist’s passion for the clouds that scudded over the Vale of Dedham as he painted. Sometimes he focussed on more intimate events but not with the level of detail that a botanist craves. We can look across the River Stour towards Flatford Mill and see the view almost unchanged from when Constable was alive. Yet, at the same time, it is almost wholly different. It is a matter of perspective …
Yallop, M., Hirst, H., Kelly, M., Juggins, S., Jamieson, J. & Guthrie, R. (2009). Validation of ecological status concepts in UK rivers using historic diatom samples. Aquatic Botany 90: 289-295.