Anatomy of the Ophioglossaceae. L 
229 
they appear in a pith which lower down was delimited by an internal endo- 
dermis, and might therefore be supposed to have been derived by cortical 
intrusion. The development of these tracheides throughout the pith thus 
strengthens the evidence against the cortical nature of the pith in Bo try - 
chium. 
The origin of the stele of 
the branch and its relations to 
the subtending leaf-trace have 
been considered. The branch 
stele soon assumes the characters 
of a complete and independent 
stele with a large pith (Text- 
fig. 10, g), from which the scat- 
tered tracheides present lower 
down (e, f) have disappeared. 
Surrounding the pith is a wide 
zone of xylem with tracheides 
in radial rows, conjunctive tissue 
and phloem ; the external endo- 
dermis is complete, and there is 
no trace of an internal endoder- 
mis. The branch stele is much 
larger than that of the main 
axis, and resembles in structure 
an adult rhizome with primary 
and secondary xylem. From this 
bulky stele two root-traces are 
first given off (Text- fig. 10, g y 
h), and then a first and second 
leaf-trace above these two roots 
respectively. There is nothing 
to indicate that the bulky pith 
in the lower part of the stele is 
of cortical origin. The gap left 
by the departure of the first leaf- 
trace closes almost at once in 
the endodermis, and a little later 
in the xylem-ring. This trace 
evidently supplied a reduced leaf, 
and, though of good size at its origin, rapidly diminishes in the cortex 
when it divides into two. A vestigial bud is present in the axil of this 
leaf (Text-fig. io, i) i and this is also the case for the second trace, 
which, however, dies out before reaching the periphery of the cortex. 
Text-fig. ii. Reconstruction of the relations of 
the steles of the main rhizome and the branch in the 
first branching specimen. 
