256. MR. A. C. SEWARD AND MISS S. 0. FORD ON 
the cortical tissues, but that it forms part of the stele. The endodermal layer of Todea 
hymenophylloides, which makes its appearance here and there in the medullary region 
and is not found in the seedling stem, may be regarded as a specially modified part of 
the stelar conjunctive tissue. 
We are as yet but imperfectly acquainted with the physiological importance of 
endodermal layers; Schwendener’s interesting paper * on this subject demonstrated the 
plasticity of the endodermis as an adaptation to diverse conditions ; but we need further 
experimental work to enable us to understand the physiological functions of endodermal 
tissue. It is well known that similar tissues may be produced in regions morphologically 
distinct. The mere structure of a cell-layer is not a safe guide to morphological value. 
The lining layers in the gaps in the leaf of Monstera are epidermal in structure, but they 
are not derivatives of a dermatogen. We believe that the view of Jeffrey and Faull 
involves an assumption for which we lack adequate reasons. 
Ia Lyginodendron, which in its primary xylem agrees closely with Osmunda, and even 
more closely with Todea, there is a ring of xylem surrounding a medullary region 
consisting of parenchyma and sclerous nests. The more typical Lygenodendron stem, 
with its separate mesarch xylem strands, suggests a comparison with Todea barbara and 
T. hymenophylloides, while those stems in which the xylem forms a more continuous 
band + may be compared with 7odea superba. It is in the stele of this extinct member 
of the Cycadofilices that we recognize what we believe to be the type of structure most 
nearly allied to that of recent Osmundacez. 
We wish to express our thanks to Mr. Lynch for the pains that he has taken to supply 
us with such material as we required. 
[Since this paper was read Prof. Jeffrey's important memoir has been published in 
the Philosophical Transactions of the Royal Society ` at the time of writing we had only 
the abstract before us, Jeffrey (1901).— November, 1902. A. C. S.] 
BIBLIOGRAPHY. 
Bary, A. pe (1884).—Comparative Anatomy of Phanerogams and Ferns. Oxford, 1884. 
Booprr, L. A (1900).—On the Anatomy of the Hymenophyllacez. Annals Bot. vol. xiv. p. 455. 
Booprx. L. A. (1901).—On the Anatomy of the Schizwacee. Ibid. vol. xiv. p. 359. 
Bower, F. O. (1885).—Comparative Anatomy of the Leaf of Vascular Cryptogams and Gymnosperms. 
Phil. Trans. R. Soc. ser. B, p. 565. i 
Bower, F. O. (1889).—The Comparative Examination of the Meristems of Ferns. Annals Bot. iii. 
p. 305. 
Bowser, F. O. (1891).—Is the Eusporangiate or the Leptosporangiate the more primitive type in the Ferns ? 
Annals Bot. v. p. 109. : : 
Bower, F. O. (1899).—' The Leptosporangiate Ferns. Phil. Trans. R. Soc. ser. B, vol. 192, p. 29. 
Bregner, G. (1901).—On the Anatomy of Danea and other Marattiaceæ. Annals Bot. xv. p. 779. 
Bronentart, A. (1828).— Histoire des Végétaux fossiles. 
é Sie E ) um Ges 
Schwendener (1835). + Williamson (1890), pl. 13. fig. 1L; see also Williamson & Scott (1895), p. 721. 
