Boodle.—Anatomy of the Hymenophyllaceae. 471 
Adiantum reniforme , Linn., was examined, and it was found 
that there also the first division of the petiolar bundle at the 
base of the lamina was dichotomous. This fact does not 
favour the view that dichotomous venation is, of itself, important 
evidence of a primitive nature. 
At the node in T. reniforme the leaf-trace approaches the 
side of the stele of the rhizome, the xylem of each opens at 
the point of contact, and the two xylem bands of the petiole 
fuse with the corresponding bands of the rhizome, while the 
protoxylem of the leaf-trace passes towards the other group 
of protoxylem in the central parenchyma. The presence of 
two protoxylems in the rhizome, in Fig. 22, means that the 
section was cut not far from a node, but Fig. 23 represents 
a section cut through the region of an internode, which has 
only one protoxylem. 
The fusion of the leaf-trace with the stele is much more like 
the union of two similar structures than in Hymenophyllum. 
T. radicans , Swartz. 
The structure of the rhizome of this species is shown in 
Fig. 24. The stele has a broad pericycle, as in most other 
Hymenophyllaceae, the phloem forms a continuous ring, and 
the xylem consists of a large solid mass of tracheides inter¬ 
spersed with parenchyma, and containing two protoxylem- 
groups 1 near the centre, each accompanied by a small mass of 
parenchyma. The parenchyma-groups are easily distinguished 
in the figure, but the protoxylem-elements are not easy to 
recognize. The two protoxylem-groups are seen in most 
sections of the internode, but they fuse into one a little way 
above the node. 
The protoxylem-elements are spiral, and occur in and 
around each mass of parenchyma. Sections of the young 
internode prove that they are the first tracheides to develop, 
and that the first metaxylem differentiated is that immediately 
surrounding each group of parenchyma and protoxylem. 
Some small and rather early peripheral tracheides are some- 
1 Two protoxylem-groups are mentioned by Prantl ( 1 . c., p. 27). 
