Root of Calamites (Astromyelon Williamsonis) in transverse section
Drawn by Williamson
It is curious to note in passing that his main divisions, so far as vascular Cryptogams are concerned, correspond to the Lycopsida and Pteropsida of Prof. Jeffrey, though the suggested relation to the higher plants would not be accepted by any modern botanist. In spite of Williamson's tactical error in weighting himself with a doubtful scheme of classification, and in spite also of a faulty terminology, it is easy to see now that he had the best of the controversy, for he knew the facts about the structure of the Carboniferous Cryptogams, which his opponents, at that time, did not. They stuck to generalities, and those who take the trouble to rake the ashes of this dead controversy will at least learn that dogmatism is not confined to theology!
An interesting point is that Williamson at that time spoke of Brongniart almost as an ally[129]. The conviction that the old Lepidodendrons and Calamites were "exogenous" then seemed to him of greater importance even than his belief that they were Cryptogams. The English opposition, however, was never really formidable, and so a change of front became necessary, to meet the attacks of the powerful French school. Williamson was an energetic disputant; not content with his numerous English publications, he published, in 1882, an article in the Annales des Sciences Naturelles, entitled "Les Sigillaires et les Lepidodendrées." This was translated into French for him by his colleague Marcus Hartog, whose assistance he greatly valued. He describes this vigorous polemical treatise as "flung like a bombshell among my opponents."
In time they came over, one by one, to his views, and even the most redoubtable of the French champions Bernard, Renault, before the close of his life, had made very considerable concessions to Williamson's side of the question. There is no need to dwell on the controversy; every student now knows that the Club-mosses, the Horse-tails and the Sphenophylls of Palaeozoic times formed abundant secondary tissues homologous with those of a Gymnosperm or a Dicotyledon; the case of the Sphenophylls shows that the character was not limited to arborescent plants then any more than it is among Dicotyledons at the present day. At the same time, as Williamson maintained, these groups of plants were, broadly speaking, cryptogamic.
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[130]."
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.