(b. Down, Kent, England, 16 August 1848; d. Cambridge, England, 19 September 1925)
Francis Darwin was the third son of Charles and Emma Darwin. He was educated at home and then at Clapham Grammar School before going to Trinity College, Cambridge, in 1866. In 1869, he took a degree in mathematics, and the following year first-class honors in the natural science tripos. He entered St. George’s Hospital, London, with the intention of becoming a physician, but his interests turned to research through the influence of Dr. Klein at the Brown Institute, where young Darwin went to learn histology. He presented a thesis and obtained the M. B. degree in 1875.
From 1874, except for a brief spell of research under Julius Sachs in Würzburg and then under H. A. de Bary in Strasbourg, he spent the next eight years working as secretary and botanical assistant to his father. He lived at Down with his parents after the death of his first wife, Amy, in 1876.
Apart from two short papers on the effects of humidity and light on the growth of roots, the results of his collaboration with his father were published in 1880 in The Movement of Plants.
In France and Germany, investigations into the causes of plant curvature in response to light were mainly directed toward finding a physicochemical explanation in terms of the direct effect of light on the curving tissues. Francis Darwin, however, working with Sachs, showed that roots grew more slowly in light than in dark.
The Darwins were strongly influenced by the experimental method that had come into biology in the second half of the nineteenth century; but, at the same time, their evolutionary approach left them uncommitted to finding direct relationships between cause and effect.
In The Movement of Plants they extended the idea of irregular circumnutatory movements to explain phototropic responses. They showed that geotropisms were similar to phototropisms and demonstrated traumotropisms: the curvature away from an apical wound. Further, they showed that the mechanism of curvature in both root and shoot was the result of differential growth rates. But their most important contribution was to show that there is some matter in the apex of root and shoot which is acted on by light and gravity and which transmits its effects to other parts of the plant. The effect of the stimulus on curvature was indirect.
Francis Darwin later refined some of the experimental techniques. In 1899, for example, he devised a method of putting the tip of a root in a horizontal glass tube and found that the rest of the root grew in irregular twists in response to the continual signal from the apex to get vertical. He rejected the idea of circumnutation and showed, also in 1899, that gravity affects shoots by apical stimulus in the same way as roots. He took up the suggestion of Němec and Gottlieb Haberlandt that gravi-perception depended on the falling of starch grains. In 1903 he showed that the response was heightened if the root was kept vibrating and, in 1904, found that geotropic excitation occurred only if there was enough force to affect the starch grains.
Subsequent work by Fitting and by Boysen-Jensen proved the Darwins’ findings, by showing that a chemical substance moved from the tip to other parts of the shoot and root; in 1928, F. W. Went isolated a growth-promoting substance and showed that light caused lateral transport of the substance from the light to the dark side, so opening up the new era of plant hormones.
After the death of his father, in 1882, Francis Darwin went to live in Cambridge, where, in 1883, he married Ellen Crofts, a lecturer in English literature at Newnham College. He became university lecturer in botany and a fellow of Christ’s College and, in 1888, reader in botany. During this time his academic interests were the study of water movements in plants, the teaching of botany, and the editing of his father’s letters.
Between 1886 and 1889 the stomatal openings of the undersides of leaves had been seen under the microscope. In 1886 Darwin published his first papers on the distribution of stomata and on the transpiration of plants. In 1897 he introduced the horn hygroscope for the study of stomatal function. A later invention for studying transpiration rate was the porometer, in which air was drawn through a leaf and its velocity measured. Both these simple devices remained in use for many years.
Wiesner had suggested that the effect of light on transpiration was direct, due to its absorption by the tissues and transformation into heat. Darwin again showed cause and effect to be indirect. In 1898 he proved that red rays induced the opening of the stomata and, assuming the intensity of transpiration to be proportional to the degree of opening of the stomata, suggested that it was the stomata that controlled the transpiration rate. In fact, the behavior of stomata has proved more complicated than Darwin realized.
His successful lectures to undergraduates were published in two books: Practical Physiology of plants, written with E. H. Acton, was the first book of its kind in the English language; The Elements of Botany provided a stimulating new approach to the basic botanical principles.
Darwin collected and edited his father’s letters for publication in 1887. The work was considered one of the best collections of its kind, because of its informative arrangement and tactful annotation, and for its chapter of reminiscences of his father’s life. With the later two volumes published in 1903, they have provided the basis for all subsequent work on Charles Darwin.
For his contributions to science, Francis Darwin received many honors. He became a Fellow of the Royal Society in 1882 and served the society on its council and as foreign secretary. Soon after the death of his second wife in 1903, he retired from all official appointments but continued his botanical research. He was made an honorary Sc. D. of Cambridge in 1909, at the time of the Darwin centenary, and, in 1912, received the Darwin medal of the Royal Society. He received honorary degrees from the universities of Dublin. Liverpool, Sheffield. St. Andrews, Uppsala, Prague, and Brussels. He was knighted in 1913.
In 1913 he married Florence Fisher, the widow of Professor F. W. Maitland, and in 1920 he was once again a widower. His later publications consisted mainly of collections of earlier essays and lectures on a variety of subjects, including musical instruments, which had been a lifelong interest.
I. Original Works. Francis Darwin’s most important works on movement in plants include “On the Hygroscopie Mechanism by which Certain Seeds are Enabled to Bury Themselves in the Ground.” in Transactions of the Linnean Society of London, 1 (1876).149–167: “Über das Wachstum negativ heliotropischer Wurzeln im Licht und im Finstern.” in Arbeiten des botanischen Instituts in Würzburg, 2 (1880). 521–528: The Power of Movement in Plants (London, 1880), written with Charles Darwin: “On Geotropism and the Localization of the Sensitive Region.” in Annals of Botany, 13 (1899), 567–574: “The Statolith-theory of Geotropism.” in Proceedings of the Royal Society, 71 (1903). 362–373: “Notes on the Statolith Theory of Geotropism.” in Proceedings of the Royal Society, 73 (1904), 477–490: Lectures on the Physiology of Movement in Plants (London)1907).
His most important works on plant physiology are “On the Relation between the ‘Bloom’ on Leaves and the Distribution of Stomata,” in Journal of the Linnean Society of London, 22 (1886). 99–116: “On the Transpiration Stream in Cut Branches.” in Proceedings of the Cambridge Philosophical Society, 5 (1886), 330–367, written with R. W. Phillips: Practical Physiology of Plants (Cambridge, 1894), written with E. H. Acton; The Elements of Botany (Cambridge, 1895): “Observations on Stomata by a New Method,” in Proceedings of the Cambridge Philosophical Society, 9 (1897), 303–308: “Observations on Stomata,” in Philosophical Transactions of the Royal Society, 1908 (1898), 531–621: “On a New Method of Estimating the Aperture of Stomata,” in Proceedings of the Royal Society, 84B (1911), 136–154, written with D. F. M. Pertz: “On a Method of Studying Transpiration,” in Proceedings of the Royal Society, 87B (1914), 281–299: “On the Relation between Transpiration and Stomatal Aperture,” in Philosophical Transactions of the Royal Society, 207B (1916), 413–437.
His biographical works include The Life and Letters of Charles Darwin. 3 vols. (London, 1887), which he edited: More Letters of Charles Darwin, 2 vols. (London, 1903) edited with A. C. Seward: and The Foundations of the Origin of Species (Cambridge. 1909).
Among his many essays are: “Stephen Hales 1677–1761,” in The Makers of Modern Botany. F. W. Oliver, ed. (Cambridge, 1913). pp. 65–83: “Memoir of Sir George Darwin,” in Scientific Papers of George Darwin (Cambridge, 1916), pp. ix-xxxiii: biographical and other essays in Rustic Sounds and Other Studies in Literature and Natural History (London. 1917): Springtime and Other Essays (London.1920).
II. Secondary Literature. See A. C. Seward and F. F. Blackman. “Francis Darwin 1848–1925,” in Proceedings of the Royal Society, 110B (1932). i-xxi: W. C. D. Dampier, “Sir Francis Darwin (1848–1925).” in Dictionary of National Biography: Twentieth Century 1922–1930, J. R. H. Weaver. ed. (Oxford, 1937). 237–238; P. R. Bell. “The Movement of Plants in Response to Light.” in Darwin’s Biological Work, P. R. Bell. ed.(Cambridge, 1959): H. Meidner and T. A. Mansfield. Physiology of Stomata (London.1968).