On the other hand it has been said by a distinguished botanist that in the Fern-series secondary growth came in together with the seed. This is not strictly correct, but it is true that the plants such as Lyginodendron, which Williamson in his later publications cited as Ferns with secondary growth, have turned out to be seed-bearing. Even among the Lycopods a certain proportion of the Lepidodendreae bore organs closely analogous to seeds. These partial concessions, which may now gracefully be made to the old Brongniartian creed, do not however really affect the importance of Williamson's results, which Count Solms-Laubach has well summed up in the following words: "It was thus made evident by Williamson that cambial growth in thickness is a character which has appeared repeatedly in the most various families of the vegetable kingdom, and was by no means acquired for the first time by the Phanerogamic stock. This is a general botanical result of the greatest importance and the widest bearing. In this conclusion Palaeontology has, for the first time, spoken the decisive word in a purely botanical question[1]."
To attempt a review of Williamson's work in fossil botany would be to write a treatise on the Carboniferous Flora. In every group—Calamites, Sphenophylls, Lycopods, Ferns, Pteridosperms, Gymnosperms—his researches are among the most important documents of the palaeobotanist, and to a great extent constitute the basis of our present knowledge. At the time he wrote, the wealth of his material was absolutely unrivalled, and its abundance was only equalled by the astonishing energy and skill with which he worked it out.
As regards the Calamites, he demonstrated, to use his own words, "the unity of type existing among the British Calamites," abolishing the false distinction between Calamiteae and Calamodendreae.
Among the Sphenophyllums (although there was at first some confusion in his nomenclature) he gave the first correct account of the anatomy, and of the organization of the cone.
Concerning the Lycopods, the greater part of our knowledge is due to him. He described the structure in ten species referred
