THE ANATOMY OF TODEA. 247 
a figure illustrating the curious bending of the sieve-tubes as they pass down into 
the space between the trace and the medullary ray immediately behind it and curve 
round and pursue an obliquely vertical upward course. Fig. 34, Pl. 29, represents a 
diagrammatic view of a longitudinal section cut along the plane shown by the line ad in 
fig. 38. The parenchymatous tissue on the right belongs to the medullary ray, mr; the 
sieve-tubes, s', bend round in a loop and extend upwards at s" on the inner faee of the 
xylem of the leaf-trace, //. Two of the sieve-tubes of the group & of fig. 39 are drawn 
on a larger scale in Pl. 29. fig. 40. The photograph reproduced in fig. 50 shows the 
xylem elements bending round (as seen in a section cut in the direction indicated by 
ed in fig. 38, but at rather a higher level where the leaf-trace has passed a little farther 
out) from the stem of the leaf. The sclerous group that makes its appearance between 
the leaf-trace of the stem (text-fig. 1, $l’) is represented in fig. 50 by a single thick-walled 
element sz. The dark line pp represents rather crushed and thick phloem elements, 
and at zt the root-tracheids are seen passing out at right angles to the trace. The 
protoxylem groups met with at any level of the stem are downward continuations of the 
protoxylem of the leaf-traces, but each protoxylem strand when followed in a downward 
direction is found to gradually decrease ín size until it disappears. The strand of xylem 
in which a group of protoxylem disappears bears a constant relation to the leaf-trace in 
which the spiral elements originated; it is the left-hand compensating strand of the 
eighth leaf-trace lower down the stem. The protoxylem group entering from leaf-trace 
n+11 ends in the left-hand strand of leaf-trace 4-3; those from leaf-traces +10, 
n+9, and n+8 terminate in the left-hand strands of z--2, n+1, and n respectively 
(Pl. 29. fig. 27, pa). The single protoxylem group of a leaf-trace gradually becomes 
broader as the foliar stele passes outwards, and by repeated branching gives rise to the 
numerous endarch protoxylem groups which occur in the petiole. 
E. Leaf and Root. 
There is little to record in regard to the structure of the leaf. The broad U-shaped 
stele consists of a narrow metaxylem band, 1-2 tracheids in width, with several 
endarch protoxylem groups; this is encircled by the phloem, of which the sieve-tubes 
are smaller than those in the stele of the stem. ‘The phloem on the convex side 
of the xylem is broader than that on the concave side. Groups of mucilage-sacs 
(Pi. 30. fig. 45) occur on the concave side of the xylem in the pericycle region, and the 
parenchymatous tissue abutting on the protoxylem strands occasionally forms small 
irregular cavities (Pl. 29. fig. 36, sp) (cavity-parenchyma). The mesophyll of the lamina 
consists of loosely arranged cells of irregular shape; but in the filmy species, e. g. 
T. hymenophylloides, the lamina is composed of a central layer of one or two large cells 
in width between the upper and lower epidermis, of which the cells have papillose outer 
walls and contain numerous chloroplasts. 
A well-known feature of the leaf of the Osmundacee is the prominence of the lateral 
wings at the base of the leaf-stalk *. These basal expansions or “ stipules” consist of 
* Bower (1825). 
2N 2 
