xxxi
Perhaps the greatest result was his demonstration, after a contro-
versy extending over a quarter of a century, that the Sigillarian and
Calamarian trees of the Carboniferous period were Cryptogams. To
use his own words: "The fight was always the same: Was Brong-
niart right or wrong, when he uttered his dogma, that if the stem of
a fossil plant contained a secondary growth of wood, the product of
a cambium layer, it could not possibly belong to the cryptogamic
division of the vegetable kingdom?" Williamson ultimately suc-
ceeded in convincing his opponents, including almost all the members
even of the French school, that the plants in question are nothing
but highly orgauised Cryptogams, their secondary growth being
mainly an adaptation to arborescent habit, and by no means an indi-
cation of Phanerogamic afinities. In this controversy Williamson
had two sets of opponents; namely, those who followed Brongniart
in regarding plants with secondary growth as necessarily phanero-
gamic, and those who, while recognising the cryptogamic nature
of the plants under discussion, denied or minimised the secondary
growth itself. Williamson, in spite of occasional mistakes in detail,
was ultimately victorious on both issues; there is to-day, not the
slightest doubt that most Palwozoic Cryptogams formed, by means
of cambium, secondary tissues essentially similar to those of Dicotyle
dons or Gymnosperms, and that these plants were none the less as
truly cryptogamic as their less highly organised representatives at
the present day.
But, apart from this controversy, upon which it is superfluous to dwell longer, Williamson advanced our knowledge of the ancient plants in many directions, especially as regards the Sphenophylleæ, of which he discovered the first fructifications showing structure; the fructifications of Calamarieae and Lepidodendre; the various types of structure among the fossil Lycopods; the existence of a group on the frontier of Ferns and Cycads, &c. He made mistakes, as all do, who carry out extensive investigations in a new field, but he corrected most of them himself, and they in no way affect the permanent value of his great work in laying the secure foundations of scientific palæozoic botany.
Williamson's remarkable skill as a draughtsman added greatly to the value of his memoirs, which are illustrated almost wholly by his own hand. He was by nature an artist, and, in addition to his scien- tific drawings, painted many pleasing landscapes in water-colours during his leisure hours.
Williamson was an all-round naturalist of a type now unhappily all but extinct. He made his mark as a distinguished original
the obituary notice by Solms-Laubach, in 'Nature' for September 5, 1895; and D. H. Scott, "Williamson's Researches on the Carboniferous Flora," 'Science Progress,' December, 1895.
