On 1 November 2018, I took part in an event led by English Heritage to unveil an iconic Blue Plaque commemorating a comparatively poorly-known scientist whose exceptional achievements continue to resonate widely today: the botanist Agnes Arber (1879–1960). The plaque is on a house in Primrose Hill, London, where Arber lived before she moved to Cambridge.
Agnes Arber's great friend and mentor – and arguably her strongest influence – was Ethel Sargant (1863–1918), who briefly worked in Kew's original Jodrell Laboratory, under the direction of the then Keeper, D. H. Scott. Ethel Sargant was a pioneering cell biologist who investigated the embryology, the early stages of development, of the Martagon Lily, making innovative studies of the double fertilization event that is now regarded as the most definitive feature of flowering plants.
After she left Kew, Ethel Sargant set up a small private laboratory in Reigate which she called 'Jodrell Junior'. There, she employed the young Agnes Arber for a year as a research assistant and trained her in microscopy techniques. Agnes subsequently took up a postgraduate studentship at University College in London, but crucially it was with Sargant that she learned to investigate plant anatomy and physiology.
In her obituary of Ethel Sargant, Agnes Arber wrote that "Her natural capacity for balanced thought developed to an exceptional degree in the congenial atmosphere of the Jodrell Laboratory. This capacity – none too common, it must be confessed, among anatomists, since it has an unfortunate tendency to atrophy under the influence of the microscope – prevented her ever consenting to the divorce of structure from function ..."
These formative years also introduced Agnes Arber to two of the most important taxonomic foci of her subsequent work: monocots and gymnosperms. She wrote an influential book on Monocotyledons (in 1925), which she dedicated to Ethel Sargant, and followed this up with a more focused book on Grasses (in 1934). In these books, Arber not only described previously little-known aspects of the anatomy, development and mature structure of monocots, but also discussed the significance of her observations in understanding the evolutionary history of this important plant group. For example, she investigated the anatomy of the leaf-like structures (termed phylloclades) of Ruscus (Butchers Broom), which bear the flowers and fruits on their lower surfaces, a feature that is highly unusual for leaves. After comparing them with similar structures in related species of the same family, Arber concluded that these structures are not merely flattened stems, as suggested by some previous authors. She subsequently developed the 'partial-shoot' theory to explain the concept of the leaf, a debate that continues to the present day, increasingly addressed by modern molecular tools.
Monocotyledons have long been an important focus of my own work at Kew. Like Arber, I emphasise the importance of the "misfits" – the rare anomalies that exist in nature of species that appear to break some of the "rules" that govern plant structure in classical morphology – such as the remarkable "inside-out" flowers of the monocot Lacandonia, in which the carpels surround the central stamens. In some cases, comparative studies of such species can greatly improve our understanding of evolutionary patterns and processes, recalling the old adage that "it's the exception that proves the rule".
I co-organised the first international monocot conference here in 1993, which led to a long series of books and follow-up conferences throughout the world. It's probably fair to say that we currently know more about monocot systematics and biology relative to any other major plant group. That knowledge owes much to foundations laid in the early 20th century by Agnes Arber.
Neither Sargant nor Arber ever gained long-term formal employment, but they both managed to continue to pursue cutting-edge research throughout their lives, partly by private means and partly by modest grants. Agnes Arber in particular never allowed the fact that she was not formally employed to reduce her immense scientific output. She became only the third woman – and the first female botanist – to be elected as a Fellow of the Royal Society (1946). She was also the first woman to receive the Gold Medal of the Linnean Society (1948). Such prestigious awards are a testament to the quality of her self-generated contributions to science.
In the Preface to her Grasses book, Arber wrote: "I have not hesitated to turn aside, from time to time, down any passage of the labyrinth which has taken my fancy". To extend that metaphor, in later life, Agnes entered a philosophical (even metaphysical) region of the labyrinth that became central to her later books, including The Mind and the Eye (1954). But for me, Arber's greatest achievement was the Natural Philosophy of Plant Form (1950). In this wonderful book Arber takes us through an annotated history of the whole of botanical science from Aristotle onwards, through Goethe, and up to the mid-20th century. She finally brings us to the brink of today's technologically-driven molecular era, which of course she never really sampled. Nonetheless, her works supply us with ideas and hypotheses that remain highly relevant to modern topics involving plant evolution and development.
There are encouraging signs that this humble blue plaque may awaken deeper interest in this most remarkable of women and her achievements.