564 Notices of Memoirs — Seward 8^' Ford — Anatomy of Todea. 



to the order Synxiphosura, it leaves Strabops as the present sole 

 representative of the Eurypterida.' 



III. — On the Anatomy of Todea, with an Account of the 

 Geological History of Osmtjndace^. By A. C. Sewakd, 

 F.E.S., and Miss Sybille 0. Ford.^ 



THE anatomical structure of the genus Osmunda has been dealt 

 with by several writers, and more particularly by Zanetti in 

 an able paper published in the BotaniscJie Zeitung for 1895, but 

 the other genus of the Osmundacege has not received equal attention 

 at the hands of anatomists. Our work, which was undertaken with 

 a view to discover in what respects Todea differs from Osmunda, 

 includes the examination of Todea barbara and T. siiperba, as well as 

 the investigation of series of microtome sections of young plants. 

 The family Osmundacese is usually regarded as to some extent 

 intermediate between the Eusporangiate and Leptosporangiate ferns, 

 and in many respects the two genera Osmunda and Todea are of 

 interest in regard to the phylogeny of the various divisions of the 

 Filicinaj. 



The stem of Todea bar-bara is traversed by a single stele composed 

 of xylem groups surrounding a central pith and separated from one 

 another by medullary rays : these groups vary considerably in shape 

 and number at different levels. There may be as few as two or as 

 many as eight xylem strands in one transverse section of the stem, 

 while in Osmunda regalis the number is considerably greater. The 

 xylem strands are surrounded by parenchyma, and the sieve-tube 

 zone occupies the same position as in Osmunda. This zone, which 

 is continuous in 0. regalis, is occasionally discontinuous in Todea 

 opposite some of the xylem strands. The comparatively large 

 sieve-tubes occur in triangular patches at the outer end of each 

 medullary ray. A characteristic band of tangentially elongated 

 elements succeeds the sieve-tube zone, and this is followed externally 

 by a parenchymatous band, the outermost layer of which constitutes 

 the endodermis. The paper deals with the phyllotaxis of Todea 

 barbara, the origin of the leaf-traces, and the gradual alteration in 

 structure which the collateral leaf-trace undergoes as it passes out 

 from the stele of the stem as a horseshoe-shaped strand with one 

 protoxylem group, and gradually assumes the form of the broadly 

 U-shaped concentric stele of the petiole with its numerous proto- 

 xylem groups. The anatomy of ' seedling ' plants of Todea is 

 found to agree with that of Osmunda regalis plantlets as described 

 by Leclerc du Sablon. As bearing on the questions of relative 



1 Although Afflaspis was compared with Limidus by Professor Hall, and its 

 affinities were distinctly stated as with the Merostomata, yet most subsequent 

 writers have overlooked its true relationships and have included it in their lists 

 of trilobite genera. The family named Aglaspidaj was first employed in 1877 by 

 S. A. Miller in "The American Palaeozoic Fossils," p. 208, and the restoration 

 of the family to the Merostomata was first made by the writer in a paper entitled 

 "Outline of a Natural Classification of the Trilobites " (SUliman's Journal (4), 

 vol. iii, p. 182, 1897). 



2 Read before the British Association, Section C (Geology), Glasgow, Sept., 1901. 



