237 
Anatomy of the Ophioglossaceae. I. 
early tangential divisions in the procambium giving rise to the elements of 
primary xylem, and the slightly later ones that give rise to the tracheides 
of the secondary xylem. The secondary growth is normally not progressive ; 
under exceptional circumstances it may, however, be actively resumed. 
The central (or centripetal) primary xylem is usually only represented 
by a few tracheides at the periphery of the pith. In one wounded stem 
numerous tracheides, the position of which was clearly centripetal, developed 
throughout the pith, and tracheides in a similar position are sometimes met 
with in normal stems. 
4. The leaf-trace commonly departs as a segment of the vascular ring 
of the stele. The centripetal xylem, if present, disappears internal to the 
leaf-trace, so that the latter at its departure is an endarch collateral strand. 
In some small rhizomes the trace may depart from the ring of outer or 
centrifugal xylem, leaving the central xylem complete ; or the central 
xylem may close across the gap before the outer xylem does. In both 
cases the xylem of the rhizome appears analysed into its outer and inner 
components. 
5. The endodermis may be completed round the adaxial side of the 
departing leaf-trace, enclosing parenchyma between it and the protoxylem 
of the trace. Divisions take place in this adaxial parenchyma, and tracheides 
may develop in it ; these extend round from the curved ends of the xylem 
of the leaf-trace, and form a more or less complete ring of xylem. Indica- 
tions at least of this adaxial xylem, which is not directly continuous with 
the inner xylem of the stem, are commonly found. The adaxial xylem is 
frequently separated from the rest of the trace by continued growth of the 
parenchyma in the region of the periderm. It may, however, still be 
represented in the leaf-trace after this has entered the petiole. 
A leaf-trace departing from a stele with secondary thickening usually 
exhibits secondary growth in the lower portion of its course through the 
cortex. 
6. Under exceptional circumstances meristematic activity may com- 
mence in the pericycle, and lead to the development of a more or less 
extensive tract of pericyclic xylem outside the phloem. This has been 
found in the stem and in the departing leaf-trace. The pericyclic xylem, 
which suggests comparison with some cases of anomalous secondary 
thickening, may or may not be associated with the presence of a branch. 
7. A single vestigial bud, similar to that described by G wynne- Vaughan 
in Helminthostachys , is regularly present in the axil of every leaf of 
B. Lunaria . It is connected to the outside by an occluded slit, and remains 
embedded in the cortical tissue of the rhizome after the leaf has withered. 
8. Under special conditions, especially when the growth of the main 
axis is arrested, branches may develop in the position corresponding to the 
vestigial buds, and evidently from one or more of the latter having been 
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