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HENSLOW, JOHN STEVENS (1796–1861), botanist, the eldest of eleven children of John Prentis Henslow, a solicitor, was born at Rochester 6 Feb. 1796. Sir John Henslow, chief surveyor of the navy, was his grandfather. Henslow, who apparently inherited a taste for natural history from both his parents, was educated first at Rochester free grammar school and afterwards under the Rev. W. Jephson at Camberwell. In 1814 he entered St. John's College, Cambridge. Though already devoted to natural history, especially entomology and conchology, and studying chemistry under Cumming and mineralogy under E. D. Clarke, he graduated as sixteenth wrangler in 1818, proceeding M.A. in 1821. He became a fellow of the Linnean Society in 1818, and of the Geological Society in 1819. During the Easter vacation of the latter year he accompanied Adam Sedgwick, an intimate friend through life, on a geological tour in the Isle of Wight. This led to their co-operation in founding the Cambridge Philosophical Society. In the long vacation of 1819 Henslow took some of his pupils to the Isle of Man, and the geology of the island formed the subject of his first paper, which appeared in the ‘Transactions’ of the Geological Society. Similarly, in 1821, he explored Anglesea, describing it in the ‘Transactions’ of the Cambridge Philosophical Society. In 1822 he succeeded Dr. Edward Daniel Clarke [q. v.] as professor of mineralogy at Cambridge, and in 1824 was ordained deacon and priest, becoming curate of St. Mary the Less, Cambridge. On the death in 1827 of Thomas Martyn, in whose hands the professorship of botany had for thirty years been a sinecure, Henslow was appointed to the chair. He shortly afterwards resigned the professorship of mineralogy, and held the botanical chair for the remainder of his life. His enthusiasm rendered botany a popular subject in the university, and his excursions and soirées were attended by men of various tastes, Darwin, Berkeley, and Babington being among his pupils. Darwin, his favourite pupil, always expressed the highest regard for him. He recommended Darwin as naturalist for the Beagle, and during the five years of the voyage took charge of all the specimens sent home. So far as Henslow's own work was concerned, the chief fruit of the expedition was a ‘Florula Keelingensis,’ published in the ‘Annals of Natural History’ for 1838.

In 1832 Henslow was appointed vicar of Cholsey, Berkshire, but only resided at that place during the long vacations. In 1837 he was presented to the crown living of Hitcham, Suffolk, and in 1839 left Cambridge for that place. He had taken an active part in politics at Cambridge as a follower of Palmerston, and now turned his energies to the reform of a most neglected parish. In spite of farmers' opposition, he established schools, into which he introduced the voluntary study of botany with signal success, benefit clubs, cricket and athletic clubs, allotments, horticultural-shows, and parish excursions. At the half-yearly flower-shows he was in the habit of delivering most effectively simple ‘lecturets,’ as he termed them, mainly on some of the specimens in his varied collection of economic products. On the occasion of the parish excursions, substituted by him for the orgies known as ‘tithe dinners,’ he accompanied his parishioners to Ipswich, Cambridge, Norwich, and to the London exhibition of 1851. He further showed his interest in their well-being by the publication in 1843 of his ‘Letters to the Farmers of Suffolk,’ dealing with the economic application of manures and other practical teachings of physiology. In the same year he made the important discovery of the valuable beds of phosphatic nodules in the Suffolk Crag. Henslow was an active member of the British Association from 1832, presiding, among other occasions, over the natural history section at the heated discussion on the ‘Origin of Species’ at Oxford in the last year of his life. He was a member of the senate of London University from 1836, and as examiner in botany from 1838 insisted upon the necessity of a practical knowledge of the subject. In 1848 he took an active part in the foundation of the Ipswich Museum, a type of what a local museum should be, and acted as president of the managing committee from 1850. For the first Paris exhibition he prepared a series of specimens illustrative of the structure of fruits, for which he received a medal, a duplicate of which is now at South Kensington. At his death his large collections were mainly divided between Ipswich, Cambridge, and Kew museums. He had greatly assisted Sir W. J. Hooker in the formation of the museums at Kew. After Darwin published his ‘Origin of Species’ in 1859, Henslow visited him at Down. ‘Henslow will go a very little way with me and is not shocked at me,’ wrote Darwin to Asa Gray (18 Feb. 1860). Henslow died at Hitcham on 16 May 1861. Adam Sedgwick attended his deathbed. Henslow was buried in Hitcham churchyard. He married in 1823 Harriet, daughter of the Rev. George Jenyns of Bottisham, Cambridgeshire; she died in 1857. He left two sons, Leonard and George, both clergymen; and three daughters, Frances, the first wife of Dr. (now Sir) J. D. Hooker; Anne, married to Major Barnard; and Louisa. There is a marble bust of Henslow by Woolner in the Kew Museum, and a lithograph portrait by Maguire in the Ipswich Museum series. The name Henslovia was given to a genus of plants now referred to Lythraceæ, and Henslowia of Wallich is a genus of Santalaceæ.

Among Henslow's chief publications are: 1. ‘Catalogue of British Plants,’ 1829; 2nd edit., 1835. 2. ‘Principles of Descriptive and Physiological Botany,’ 1836, in Lardner's ‘Cabinet Cyclopædia.’ 3. An ‘Account of Roman Antiquities found at Rougham,’ 1843, now a scarce pamphlet. 4. ‘Dictionary of Botanical Terms,’ 1857, originally issued in Maund's ‘Botanic Garden.’ 5. Nine botanical diagrams issued by the Science and Art Department in 1857. His name was put on the title of a ‘Flora of Suffolk’ issued in 1860 by Edmund Skepper, without his consent, he being merely a contributor. The successful ‘Elementary Lessons in Botany’ by Professor D. Oliver (1863) is professedly based upon work left in manuscript by Henslow.

[Memoir by his brother-in-law, the Rev. Leonard Jenyns, now Blomefield, with photograph of Woolner's bust and full bibliography, 1862; Proceedings of Linnean Society, 1861, vol. xxv.; Gardeners' Chronicle, 1861, pp. 505, 527, 551; Gent. Mag. 1861, ii. 90; F. Darwin's Life of Darwin, 1888; Clark and Hughes's Life of Adam Sedgwick, 1888; art. Darwin, Charles Robert.]

G. S. B.