770 MR R. KIDSTON AND MR D. T. GWYNNE-VAUGHAN ON 



and O. cinnamomea. In these plants the young roots that arise near the growing point 

 of the stem are not able to bore their way straight out through the coating of leaf- 

 bases. The older leaf-bases near the outside appear to be too tough for them to penetrate. 

 So they eventually turn upwards and become flattened out between the closely packed 

 leaf-bases. At the same time they branch copiously in a distichous manner. Many 

 of these roots never reach the soil until the old leaf-bases lying outside them rot away. 

 Some of them, however, may do so by growing on upwards until they have over-topped 

 the coating of leaf-bases. 



Osmundites skidegatensis, Penhallow. 



Plate IV., figs. 22, 23, and Plate V., figs. 24-28. 



1902. Osmundites skidegatensis, Penhallow, Trans. Roy. Soc. Canada, ser. 2, vol. viii. p. 3, pis. i.-iv., 



figs. 1-8. 

 1902. Osmundites skidegatensis, Penhallow, ibid. p. 32, pis. vii.-xi. 



Our attention was first drawn to the remarkable structure of this plant by the inspec- 

 tion of the admirable photographs given by Professor Penhallow in his original descrip- 

 tion of the species, and on communicating with him he at once most generously presented 

 us with a transverse section of his fossil. A photograph of this section is shown on 

 PI. IV, fig. 22. The section includes but little more of the stem than the stele itself, and 

 since this alone measures as much as 2*4 cm. in diameter, it follows that the whole 

 stock, with its coating of leaf-bases, must have been very much larger than that of any 

 known member of the Osmundacese. The structure of this plant has such an important 

 bearing upon the discussion of the vascular morphology of the order that it is necessary, 

 even at the risk of some repetition, to deal with it here in full detail, in order that a 

 proper appreciation of its relation to the other species may be attained. 



Structure of the Stem. 



The xylem ring of the stele contains about fifty very distinctly separate strands, and, 

 so far as the relation of these strands to one another and to the entering leaf-traces is 

 concerned, it clearly belongs to the type represented by Osmunda regalis. The xylem 

 ring surrounds a very wide pith (PI. IV., figs. 22 and 23, P.), which consists partly of 

 thin-walled and partly of thick-walled sclerotic cells. The latter occur in scattered 

 groups of various forms and sizes. The most startling point in its anatomy, however, 

 is the fact that the departure of each leaf-trace interrupts the continuity of the whole 

 vascular ring. Not only is there a gap left in the xylem ring, but also in the phloem, 

 and through this gap the tissue of the pith becomes perfectly continuous with that of 

 the cortex in the axil of the leaf-trace (PI. IV., fig. 22, b., fig. 23, lg., and PI. V., fig. 25). 

 But this is not all, for the inner margin of the xylem is surrounded by a ring of in- 

 ternal phloem (PL IV., fig. 23, int. ph., and PI. V., figs. 24, and 27, int. ph.), and at the 



