A natomy of the Ophioglossaceae . /. 213 
xylem ring the internal endodermis appears. This soon forms a complete 
ring, as seen in transverse sections, but the first appearance of the endo- 
dermal markings is irregular and the internal endodermis does not form 
a closed pocket at the lower end. As the distance widens between the 
leaf-trace and the xylem of the stele, both being still enclosed by the ex- 
ternal endodermis, endodermal markings appear on the walls of cells 
connecting the outer and inner endodermal layers. Thus on the separation 
of the leaf-trace, first on one side and then on the other, both the trace 
and the vascular tissue of the stem have complete endodermal sheaths. 
That of the stem consists of the external endodermis connected round the 
margins of the leaf-gap with the internal endodermis. Above the departure 
of the leaf-trace first one and then another root-trace arises from the stele. 
At the upper end of the leaf-gap the incurved ends of the external endo- 
dermis approximate, and this again becomes a complete and independent 
tube. The internal endodermis persists for a short distance as an imperfect 
tube, but all endodermal markings have disappeared from the pith before 
the gap in the xylem closes. Above this remarkable leaf-insertion the 
stele increases in diameter, and the xylem ring is thicker and shows 
secondary thickening. A number of leaf-traces are given off with com- 
paratively short intervals between them, the endodermal relations at their 
departure, like the general features of the stele, being of the adult type. 
The last of the six plants (Plant F) shows much in common with the 
preceding specimen. Its structure is illustrated by the reconstruction 
of the stele (Text-fig. 8) and by the series of selected transverse sections 
in Text-fig. 9. The numbers 1-2 1 refer to the slides of this series, on each 
of which an equal number of sections was mounted ; where the changes 
were rapid and several sections from one slide are figured they are dis- 
tinguished by letters, e. g. 2 a, 2 b, 2 c, 2 d . Comparison of this series of 
sections with the reconstruction will make the relations of this rather 
complicated plant clearer, and will also show the general nature of all the 
reconstructions. 
The first root was in line with the base of the stem, and the stele 
of the root when followed up passed into the solid core of xylem of the 
stem stele (Text-fig. 9.7). This increased in diameter and showed a zone of 
tracheides radiating from a central group ; a root is attached in this region 
(2 a). Parenchyma appears mingled with the central tracheides (2 b ) and 
soon forms a distinct pith (2c, 2d). After two roots have been attached 
a small leaf-gap with no evident departing trace forms in the xylem ring, 
but a trace is recognizable close to the periphery of the cortex, haying 
apparently been separated by the cortical growth (Text-fig. 9. y Compare 
the reconstruction, Text-fig. 8). When this gap has closed, two roots, one of 
which is shown in Text-fig. 9 . y arise from the stele. Then another root-trace 
arises fb). and immediately above this the second leaf-trace separates (j”, 6 ). 
