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 and invaluable. Early researches on the Foraminifera between 1840 and 1850 led to his preparing a monograph on the recent forms of this group for the Ray Society; William Benjamin Carpenter [q. v.] asserted that his work introduced a new technique for their study (that of thin sections) and a new conception (that of the combination of a wide variety of forms hitherto ranked as of specific or generic rank in single individuals), and that it gave a starting-point for all future investigations. Researches on Volvox about 1850, only some thirty years later noticed and confirmed, demonstrated that this critical form is essentially vegetal, not animal, in its morphology. A very complete study of the wheel-animal, Melicerta, was published in 1853, and in consequence he was employed by Andrew Pritchard to write a monograph on the Rotifera for the third edition of his ‘Infusoria’ (1861); this was an admirable compilation. Between 1840 and 1850, largely provided with material by Sir Philip de Malpas Grey-Egerton [q. v.], he produced two monographs on the histology of teeth, fish scales, and bone, of classical value. Herein he demonstrated two capital theses—the essential identity of teeth and of fish scales, and the distinction of bone formed directly in membrane from that preformed in cartilage. Kölliker, the great histologist, esteemed the work important enough to warrant his arduous pilgrimage from central Germany to accept Williamson's hospitality of board and study. This work gained Williamson the fellowship of the Royal Society (1854). Fossil plants had engaged his earliest efforts. He resumed their study in 1854 with the enigmatic form Zamia gigas, called Williamsonia by W. Carruthers, who says that Williamson has probably come closer to its determination than any one else. But it was only towards 1858 that he really began that comprehensive study of the plants of the coal-measures which is his greatest claim to rank as one of the founders of palæobotany. He demonstrated that with certain characters of the higher existing flowerless plants—horsetails, ferns, clubmosses, &c.—there were found at that period plants whose woody cylinder grew by external deposit of new layers, as in our forest trees. His results met at first with neglect and hostility. His drawings were exquisite and nature-true, made on lithographic transfer paper with the artifice of a quadrillé eye-piece; but they suffered in the processes of transference to stone and printing. His figures were distributed over the plates with a view rather to neatness and economy of space than to logical connection. In each successive memoir he described all the material he had studied completely up to date. To his unfamiliarity with modern botanical terminology he added a defective exposition. His text was a detailed description of the specimens, with references to the accompanying plates and to those of previous memoirs, interspersed with discussions of generalities and of controversial matter, without tables of contents, general introductions, or final summaries and conclusions. To master such papers was, in effect, to conduct a research on the figures with a minimum of effective aid. In 1871 a discussion at the British Association was followed up in ‘Nature,’ where a correspondent accused him of going back to the conceptions of Nehemiah Grew [q. v.] In France his results were systematically ignored, despite his constant invitations to his opponents to study his specimens as his guests, until 1882, when for the first time the facts and arguments on both sides were marshalled in a readily accessible form in a French essay, ‘Les Sigillaires et les Lépidodendrées’ by Williamson and his demonstrator, Professor Marcus Hartog (Ann. Sc. Nat. 1882). Fresh evidence poured in. In 1887 Renault, his chief opponent, retreated honourably from one part of the field, and Grand' Eury and Saporta in 1890 avowed their general conversion. Only in respect of one minor point—the question of the interstitial growth of the centre of the woody cylinder—did Williamson's views break down; but it was through his own laborious investigations that the disproof was completed. A full investigation on the structure of compact coal was commenced in 1876 and continued to his death, but the examination of many thousand sections led to no publication embodying general results after the preliminary note (British Association Report, 1881). A valuable research in 1885 extended Nathorst's discovery that reputed animal and vegetable fossils were mere tracks of animals or of tidal currents. Williamson never spared money in the purchase of adequate apparatus and specimens; one of the latter, a magnificent Sigillaria with stigmarian roots, from Clayton, near Bradford, now in the Manchester Museum, was long called ‘Williamson's Folly.’ He met with generous help from the amateur field-naturalists of the north, often working men, who were proud to help him with the fossils they had collected or the sections they had cut and noted as worth his study. This help he always acknowledged.

Williamson's scientific work lacked, of course, the method developed by personal academic training and by the laboratory