the world--have afforded conclusive proof of this mode of growth of _Sigillaria_ and _Stigmaria_. [118] _Quart. Journ. Geol. Soc._, vol. ii. p. 394 (1846); _Ibid._, vol. iv. p. 47 (1847); _Ibid._, vol. v. p. 355 (1849); _Ibid._, vol. v. pp. 23, 30. [119] Williamson has noticed this in his excellent Memoirs in the _Phil. Trans._ "The objection to calling the Stigmariæ roots and their processes rootlets, appears to me a finical application of modern botanical usages to times for which they do not hold. We might equally object to the application of the term roots to those which spring from the earthed-up stems of Calamites, radiating as they do from nodes which, in the air, would produce branchlets. Grand' Eury's figures show abundant instances of this. We might also object to the exogenous stems described by Williamson, which belong to cryptogamous plants; and, unlike anything modern, are made up exclusively of scalariform tissue. If the articulation and regular arrangement of those gigantic root hairs, the rootlets, or 'leaves' of _Stigmaria_, are to be regarded as depriving them of the name which clearly describes their function, we may call them underground branches, though, by so doing, we set at nought both their function and their mode of growth." Dr. Williamson, in a recent paper, expresses the same view in the following terms[120]:--"At that period (the Carboniferous age) no Angiosperms existed on the earth, and even the Gymnosperms were very far from reaching their modern development. Under these circumstances the Cryptogams chiefly became the giant forest trees of that remote age. To become such, they required an organization very different in some respects from that of their degraded living representatives. Hence we must not appeal to these degenerate types for illustrations and explanations of structures no longer existing. Still less must we turn to what we find in the Angiosperms, that wholly distinct race which has taken the place of the primæval Cryptogams in our woods. The primeval giants of the swampy forests had doubtless a morphology assigned to them, adapted to the physical conditions by which they were surrounded; but if even their dwarfed and otherwise modified descendants fail to throw light upon morphological details once so common, still less must we expect to obtain that light from the living and wholly different flowering plants." [120] _Natural Science_, July, 1892.