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Promoting Irish Culture and History from Little Rock, Arkansas, USA


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Birth of Henry Dixon, Biologist & Professor

Generated by IIPImageHenry Horatio Dixon, plant biologist and professor at Trinity College, Dublin, is born in Dublin on May 19, 1869. Along with John Joly, he puts forward the cohesion-tension theory of water and mineral movement in plants.

Dixon is the youngest of the seven sons of George Dixon, a soap manufacturer, and Rebecca (née Yeates) Dixon. He is educated at Rathmines School and Trinity College, Dublin. In 1894, after studying in Bonn, Germany, he is appointed assistant and later full Professor of Botany at Trinity. In 1906 he becomes Director of the Botanic gardens and in 1910 of the Herbarium also. He has a close working relationship with physicist John Joly and together they develop the cohesion theory of the ascent of sap.

Dixon’s early research includes work on the cytology of chromosomes and first mitosis in certain plants. Familiarity with work on transpiration and on the tensile strength of columns of sulfuric acid and water leads Dixon and Joly to experiment on transpiration. “On the Ascent of Sap” (1894) presents the hypothesis that the sap or water in the vessels of a woody plant ascends by virtue of its power of resisting tensile stress and its capacity to remain cohesive under the stress of great differences of pressure. Dixon and Joly further demonstrate that water is transported through passive vessels and not living cells.

Dixon writes Transpiration and the Ascent of Sap in Plants (1914), which brings various theories and experimental works together in a coherent argument. He also writes a textbook, Practical Plant Biology (1922).

In 1907 Dixon marries Dorothea Mary, daughter of Sir John H. Franks, with whom he raises three sons. He is the father of biochemist Hal Dixon and grandfather of Adrian Dixon and Joly Dixon.

In 1908 Dixon is elected a Fellow of the Royal Society. In 1916 he is awarded the Boyle Medal of the Royal Dublin Society. He delivers the society’s Croonian Lecture in 1937.

Henry Dixon dies in Dublin on December 20, 1953.

(Pictured: Henry Horatio Dixon, bromide print by Walter Stoneman, 1922, National Portrait Gallery, London)

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Birth of Matilda Cullen Knowles, Pioneer in Irish Lichenology

matilda-cullen-knowlesMatilda Cullen Knowles, considered the founder of modern studies of Irish lichens following her work in the early twentieth century on the multi-disciplinary Clare Island Survey, is born on January 31, 1864 in Cullybackey near Ballymena, County Antrim, Northern Ireland. Her work is said to have “formed an important baseline contribution to the cryptogamic botany of Ireland and western oceanic Europe.”

Knowles’ early interest in botany is encouraged by her father, William James Knowles, himself an amateur scientist who takes Matilda and her sister to meetings of the Belfast Naturalists’ Field Club. This is where she first meets Robert Lloyd Praeger who continues to be a lifelong influence. In 1895 she is introduced to the Derry botanist Mary Leebody and together they work on a supplement to Samuel Alexander Stewart‘s and Thomas Hughes Corey‘s 1888 book the Flora of the North-east of Ireland.

Knowles then volunteers to help with the crowdsourcing of material about the plants of County Tyrone. While completing this work Knowles publishes her own first paper about Tyrone’s flowering plants in 1897. She eventually sends in over 500 examples that are considered for inclusion in the Irish Topographical Botany, which Praeger publishes in 1901.

In 1902, after attending the Royal College of Science for Ireland for a year, Knowles is appointed a temporary assistant in the then Botanical Section of the National Science and Art Museum. She works closely with Professor Thomas Johnson to continue the development of the Herbarium collection. She also co-authors with him the Hand List of Irish Flowering Plants and Ferns (1910).

One of Knowles’ first works is The Maritime and Marine Lichens of Howth, which the Royal Dublin Society publishes in 1913. Knowles had gathered the knowledge and experience to do this while diligently assisting with a survey of Clare Island as suggested by Praeger. This novel survey involves not only Irish but also several European scientists including prominent UK lichenologist, Annie Lorrain Smith. This is claimed as the most extensive piece of field work at the time. As a result, Knowles is able to create a foundation for her later specialism in lichens.

Knowles publishes more than thirty scientific papers on a wide range of botanical subjects between 1897 and 1933. It is while studying the lichens of Howth that she discovers how lichens by the shore grow in distinct tidal zones that can be distinguished by their colour: black, orange and grey.

Her major work is The Lichens of Ireland which adds over 100 species of lichen to the Irish List and records the distribution of the eight hundred species identified in Ireland. She achieves this task with the collaboration of thirty other natural scientists. It is published in 1929 and includes twenty lichens that had previously not been identified as Irish.

Professor Thomas Johnson retires in 1923, allowing Knowles to take over curatorship, working with Margaret Buchanan. As she becomes older Knowles’ hearing begins to fail such that she has to rely on an ear trumpet. Despite her deafness she still attends meetings. She cares for and adds to the National Museum Herbarium collection although never gets the credit she deserves. In 1933 she plans to retire but pneumonia ends her life before she ends her career. Knowles dies in Dublin on April 27, 1933.

Knowles is honoured with a commemorative plaque by the Irish National Committee for Science and Engineering in October 2014 to mark the 150th anniversary of her birth.