THE ANATOMY OF TODEA. 247 
INTERNAL STRUCTURE. 
A. Seedling. 
The anatomy of the early stages in the development of the sporophyte of 
Osmunda regalis was described by Leclere du Sablon in 1890*, and Faulls recent 
paper in the ‘ Botanical Gazette’ contains a brief description of the stele as seen in a 
transverse section of a young plant of O. Claytoniana t. Our examination of the seedlings 
(Pl. 27. fig. 10) of Todea hymenophylloides shows that this species of Todea agrees 
in essential respects with Osmunda regalis. Near the apex of the primary root the stele 
includes two groups of xylem separated by a central group of unlignified elements 
(Pl. 28. fig. 22); at a slightly higher level a single diarch plate is formed by the union 
of the two protoxylem strands (fig. 24). The next stage is shown in fig. 20a; the 
centre of the stele is now occupied by a solid tracheal strand surrounded by thin-walled 
tissue, limited externally by an ill-defined endodermis. A protoxylem strand, indicating 
the position of a leaf-trace, is shown, as pz, in a mesarch position. The endodermis is 
succeeded internally by a layer of parenchyma, the radial walls of which alternate with 
those of the endodermal layer, and this band of cells is separated from the nucleated 
parenchymatous elements by a layer of sieve-tubes. The whole is enclosed in a mass of 
sclerenchyma. At a higher level the stele is larger and the central tracheids have given 
place to a small island of parenchyma (PI. 28. fig. 25, m). The irregular endodermis is 
seen at ez, succeeded by nucleated cells, pr, occupying the position of the pericycle ; 
internal to these the sieve-tubes, s, are easily recognized, separated by parenchymatous 
elements, xp, from the scalariform tracheids ; the smaller elements, px, probably indicate 
the position of the protoxylem of the leaf-trace, l£. 
Plate 30. fig. 48 shows a stele with a larger medullary region, m, and three outgoing 
leaf-traces ; the endodermis is seen at en. The leaves are crowded in the young stem, 
and the passing out of a leaf-trace from the small medullated stele does not necessarily 
break the continuity of the xylem ring; in other words, leaf-gaps are not formed until we 
reach a slightly higher level. This is illustrated by fig. 200; the medullary parenchyma 
is larger than in the stele represented in fig. 25; a leaf-trace with its protoxylem, p2,-is 
on the point of freeing itself from the stele at Jt, and at //' another trace is beginning to 
bend out. At a higher level, fig. 20 c, the xylem band is broken and the overlapping 
foliar gaps produce an appearance characteristic of the older form of stele. We have 
not discovered any trace of an endodermal layer in the medullary region of the seedling 
stele. The stele of a young plant or “ crown ” borne on an old massive stem of Todea 
barbara is represented in Pl. 30. fig. 52; the xylem exhibits the structure and arrange- 
ment of the mature stem on a small scale, and the pith consists of a homogeneous 
parenchyma without any indication of an internal endodermis in the perimedullary 
region. 
* Leclerc du Sablon (1890), p. 9. + Faull (1901), p. 387, pl. 17. fig. 23. 
+ We use this term, in spite of its inaccuracy, in preference to “ sporeling." 
