THE ANATOMY OF TODEA. 249 
tracheids of the metaxylem of Megalozylon*. The tangential elongation of the elements 
external to the larger sieve-tubes is less marked than in 7. barbara. "The endodermis 
forms a more clearly defined layer, and its position is often clearly shown by the 
readiness with which its cell-walls are broken in the process of section-cutting (fig. 32, 
en). The structure of the apical region of the stem of Todea superba has already been 
described (figs. 14, 19, & 21), and reference has been made to the more pronounced mesarch 
character of the xylem groups. The manner of exit of the leaf-traces (figs. 29, 35) is 
similar to that described in 7. barbara. In the diagram shown in fig. 35 the broad band of 
sieve-tubes, s, represents the phloem of the stem which bends up as a loop to give off a 
branch to the outgoing leaf-trace (shown at a later stage in Todea barbara in Pl. 29. 
fig. 39, s’). The roots are frequently given off from the xylem before it has left the stele 
of the stem, and the two formed in connection with each leaf-trace do not arise at the 
same level (fig. 29, Pl. 29, 7). 
The dark band (8) shown in fig. 32 is due to a brown deposit in the region of the 
tangentially elongated elements as seen in a section taken from the basal region of the . 
stem, where the tissues showed signs of decay. 
TODEA HYMENOPHYLLOIDES.—One plant of this species was examined in which the 
stele could be traced for a distance of about 2 cm. In its widest part the stele had a 
diameter of nearly 3mm. The xylem is characterized by the greater number of the 
strands (Pl. 30. fig. 44) as compared with 7. superba; there may be as many as ten or 
eleven in the upper region of the stem, but towards the base the number gradually 
decreases until the xylem eventually appears as a ring enclosing a central pith (fig. 37, 
Pl. 29). The form of the xylem near the base of the stem, shown in fig. 37, is practically 
identical with that of the seedling stele represented in fig. 48; in neither case is there 
any indication of an internal endodermis. As shown in Pl. 80. figs. 44, 46, 47, and 49, 
the xylem strands appear either as oval groups, with or without protoxylem elements 
(fig. 46), or as U-shaped groups which are about to give off the outer portion as a leaf- 
trace. The protoxylem is always mesarch, and nearer the outer edge of the xylem 
group than in the other species examined; this near approach to the exarch structure is 
clearly shown in fig. 47. A few unusually large tracheids, similar to those in T. superba 
(figs. 30 & 31), were met with in the xylem strands of T. hymenophylloides. The large 
clear sieve-tubes form groups in the outer part of the medullary rays (s, figs. 17, 44, 46, 
47), and agree closely in arrangement with the sieve-tubes of the other species. The 
tangentially elongated elements (Pl. 28. fig. 17, /) are very similar to those in 7. superba. 
The endodermis is clearly marked, but the suberization is not always confined to cne 
cell-layer (Pl. 28. figs. 15 & 17, en). Todea hymenophylloides is characterized by having 
an internal endodermis; this occurs as an irregular layer of cells with suberized walls 
(P 1. 29. fig. 28, en; Pl. 30. fig. 44, en'). It is noteworthy that this inner endodermis 
does not form a very compact or well-marked layer; it was found in a few sections near 
the apex of the stem, and here and there in the peripheral region of the pith in the 
lower part of the stele, but it is by no means continuous, The suberization is not 
* Seward (1899). 
