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 Rh to Lepidodendron, besides other allied forms, and placed our knowledge of the comparative anatomy, once for all, on a broad and secure basis. His great monograph of Stigmaria, by some considered his best work, is still our chief authority for the subterranean organs.

In the Ferns he made important contributions to our knowledge of the group now familiar to botanists as the Primofilices of Arber. In particular his account of the plant now known as Ankyropteris corrugata is still among the best we possess of any member of the family.

In Pteridosperms, to use the modern name, Williamson may fairly be called the discoverer of the important family Lyginodendreae. He appreciated their intermediate position, speaking of them, in 1887, as "possibly the generalised ancestors of both Ferns and Cycads."

As regards both Pteridosperms and Gymnosperms proper, attention may be specially called to his work on isolated seeds, in which he was surpassed by Brongniart alone. This field of investigation, long neglected, has lately been revived with striking results.

I hope that all students of fossil botany will have at least turned over the pages and the plates of Williamson's works, for only by inspection of the original memoirs can any idea be gained of his vast services to our science.

His remarkable skill as a draughtsman (for all his memoirs are illustrated by his own hand) is not always done justice to in the published reproductions as the fine examples of his original drawings, so kindly lent for the lecture by Mrs Williamson, will show. At the time when Williamson's main work was in progress from 1870 to 1892 geologists were probably more appreciative of its value than botanists. Happily, in spite of occasional trouble with Referees, none of his work was lost, the Royal Society going steadily through with all the nineteen memoirs which were entrusted to them.

The one botanist, who, up to the year 1890, estimated Williamson's work at its full value was Count Solms-Laubach,