"In Zoology, Williamson initiated the work done in the study of _deep-sea deposits_, by his remarkable memoir on the mud of the Levant, in 1845, when he was 29 years old. This led to his study of the Foraminifera (especially by the aid of thin sections) and to his monograph in the Ray Society on that group.... "Of his contributions to Botany through his sections of 'Coal balls' I need say nothing." Prof. Judd makes no reference here to the papers which obtained for Williamson his F.R.S. in 1854. These embodied his researches on the development of bone and teeth, in which he demonstrated that the teeth are dermal appendages homologous with the scales of fishes. This important work dated back to 1842 and was inspired by his enthusiasm for the then novel cell-theory of Schleiden and Schwann. The interest aroused by this investigation is shown by the fact that the great German anatomist Kölliker travelled to Manchester, about the year 1851, to see Williamson's preparations. As regards Williamson's work as a botanist, in which we are chiefly interested in this course, his best contribution to recent botany was no doubt his investigation of _Volvox_, published in 1851 and 1852, in which he traced the development of the young spheres and the mode of connection of their cells, anticipating the results of much later researches. He was a great lover of living plants; his garden and greenhouses at Fallowfield, his Manchester home, were of remarkable interest, and he was a keen gardener. At the British Association Meeting of 1887 one of his guests said that "most of the distinguished botanists of Europe and America were in the garden, and not one but who had seen something growing he never saw before[126]." Insectivorous plants and the rarer vascular cryptogams were specially well represented. It was from his private garden that his classes were supplied with specimens. As we have seen, fossil plants engaged Williamson's attention in his earliest years, when as a mere boy he contributed to Lindley and Hutton's _Fossil Flora_. His first important independent work in this field was his paper "On the Structure and Affinities of the Plants hitherto known as Sternbergiae" (1851), in which he proved, for the first time, that these curious fossils, resembling a _rouleau_ of coins, were casts of the discoid pith of _Dadoxylon_, or, as we should now say, of Cordaiteae--the first step in the reconstruction of this early gymnospermous family. This investigation, to which he appears to have been led almost accidentally, through some good specimens coming into his hands, brought him back, as he says, to his old subject of fossil botany. It was long, however, before he got fairly started on his great course of investigations on Carboniferous plants.