^{page 455 note *} Part I., Trans. Roy. Soc. Edin., vol. xlv., part iii. (No. 27), pp. 759–780Google Scholar, pls. i–vi., 1907. Part II., idem, vol. xlvi., part ii. (No. 9), pp. 213–232, pls. i–iv., 1908. Part III., idem, vol. xlvi., part iii. (No. 23), pp. 651–667, pls. i–viii., 1909.

^{page 456 note *} Seward, and Ford, , “Anatomy of Todea, etc.,” Trans. Linn. Soc. Lond., Ser. II., Bot., vol. vi., 1903, pl. xxix. fig. 29Google Scholar.

^{page 461 note *} Seward, , “Fossil Plants from South Africa,” Geol. Mag., N.S., decade v., vol. iv. p. 482, 1907CrossRefGoogle Scholar.

^{page 461 note †} Stur, , “Beit. z. Fl. d. Süsswasserquarze im Wien im Ung. Beck.,” Jahrb. d. K. K. geol. Riechanst., vol. xvii. p. 136, 1867Google Scholar.

^{page 464 note *} Fossil Botany, English ed., p. 172.

^{page 466 note *} Das Leitungsystem im Stamen von Osmunda regalis und dessen Übergang in den Blattstiel, pp. 25–26, 1895.

^{page 467 note *} The striking similarity between these fossils and the stocks of the modern Osmundaceæ, even when judged superficially by the external appearance alone, has been pointed out by Mr Carruthers, although he does not go so far as to include them in the order (Carruthers, , Quart. Journ. Geol. Soc., vol. xxvi. p. 352, 1870)Google Scholar.

^{page 467 note †} Scott, , Studies in Fossil Botany, 2nd edit., p. 291, 1908Google Scholar; Renault, Gours de botanique fossile, pl. xxi. figs. 12–14, 1883; Zeiller, (1) “Étude sur la flore fossile du Bassin Houllier d'Héraclée,” Mém. Soc. Géol. de France, Mém. 21, p. 21, 1899: (2) Éléments de palébot., p. 65, 1900; Bower, “Is the Leptosporangiate or the Eusporangiate the more primitive type of Ferns?” Ann. Bot., vol. v. p. 126, 1891Google Scholar.

^{page 467 note ‡} The idea of a direct transformation of the central xylem of a protostele into parenchyma and other tissues has already been put forward by L. A. Boodle in the Schizsæaceœ: 1, “On the Anatomy of the Schizæaceæ” Ann. Bot., vol. xiv. p. 410, 1901; 2Google Scholar, “Further Observations on Schizæa,” Ann. Bot., vol. xvii. p. 530, 1903Google Scholar.

^{page 468 note *} Incidentally this conception of a direct, in situ, metamorphosis of primary xylem into pith, if carried a point further, may throw some light upon the unusual structure of the primary xylem of the stems of Pitys antiqua and Calamopitys fascicularis as described by Dr Scott (Trans. Roy. Soc. Edin., vol. xl., part ii. (No. 17), p. 331, 1902)Google Scholar. These stems possess a pith surrounded by a large amount of secondary xylem. A certain amount of primary xylem is also present in the form of isolated strands with mesarch protoxylems situated in the pith at a considerable distance from the inner margin of the secondary xylem.

It is possible that this may be accounted for by supposing that the protoxylems were originally immersed in a continuous zone of xylem, and that not only has the metaxylem lying between them become converted into pith, but also the greater part of that lying to the outside of them. So that all that is left of it is a few elements in immediate relation to the protoxylem strands themselves, which remain in their original immersed positions, and are now surrounded by pith instead of metaxylem.

^{page 468 note †} The Evolution of the Filicinean Vascular System, p. 105, 1908Google Scholar.

^{page 468 note ‡} Gordon. Described in paper read at Roy. Soc. Edin., 20th Dec. 1909Google Scholar.

^{page 469 note *} Études sur la fronde des Zygoptéridees, Lille, 1909Google Scholar.

^{page 471 note *} The vascular strands that we have observed to be given off from the free petiole of Zygopteris corrugata are all so small that they can hardly have supplied appendages of more importance than mere scales. Dr Scott figures the insertion of such a scale near the base of a petiole, and compares it with an “aphlebia” (Studies in Fossil Botany, p. 313). All the departures that we have seen suggest the same sort of thing. In fact, the occurrence of a fully developed pinna-trace equivalent to that of Zygopteris bibractensis has not yet been described in Zygopteris corrugata; indeed, it is possible that none such existed.

^{page 473 note *} Gordon. See note, p. 468.