478 Boodle,—Anatomy of the Hymenophyllaceae. 
Fig. 42 represents some bordered pits of a tracheide. They 
were drawn on account of their unusual shape. One or two 
tracheides with similar pits were seen in this species. The 
other tracheides are of the usual scalariform type as in other 
species of the genus. The pits illustrated differ from typical 
structure in their narrowness and in the large size of the 
border. 
T. heterophyllum , H.B.K. 
This is a species with a creeping rhizome, but it has a stele, 
which appears to be of the same type as T, spicatum , but the 
tracheides are larger. In the dried material examined the 
position of the protoxylem could not be determined, but it 
appeared that no spiral elements were present. 
T. scandeus, Linn. 
The stem of this species is a creeping rhizome, and has 
a large stele. The tracheides are large and separated by a 
network of parenchyma (Fig. 38), and the protoxylem con¬ 
sists of small spiral tracheides (px) which are scattered round 
the periphery of the xylem. Sections of a young rhizome 
proved that these were the first tracheides to differentiate. 
Thus T. scandeus differs from all the species described above 
in having a circular mass of xylem, with distinctly peripheral 
protoxylem. 
The petiole has a bundle with a slightly arched xylem-mass. 
As seen in the young stage (Fig. 39), there are three proto- 
xylems (px 1 ). The phloem is interrupted on the upper side, 
and it appears to be just interrupted by the median proto- 
xylem-group. The leaf-trace in the stem probably has 
peripheral protoxylem on its outer side. At the node some 
spiral tracheides were seen on the outer side of the leaf-trace, 
and continued downwards at the periphery of the stele of 
the stem. 
T. apiifotium , Presl. 
This species has a larger stele, which appears to be of the 
same type as T. scandeus. 
