Henry 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)