ANATOMY 461 
the stem of the young plant, but fades off in the upper regions, as in 
Ophioglossum. 
- In transverse sections of the stock of Botrychium, in which “the leaf- 
gaps are limited in area and not so closely placed as in Ophioglossum, 
the vascular ring is often seen to be complete, or where a leaf-trace issues 
it may be interrupted: the xylem is endarch. Much importance has 
been accorded to the secondary thickening seen in both stem and root 
of Botrychium. A sluggish cambium appears between the phloem and 
xylem, and may even be seen to be active close below the apex before 
either of those tissues are differentiated: it adds fresh tracheides to the 
xylem, but little or nothing to the, phloem, while the radially seriated wood 
Fic. 258. 
Ophioglossum Bergianum, Schlecht. A =transverse section ot the stock, showing a 
large semilunar stele, with wide foliar gap into which a small leaf-trace strand is entering. 
#=another section, showing probably the result of overlapping of the foliar gaps. X 200. 
is traversed by parenchymatous rays. The secondary activity extends also 
into the basal region of the root, but it does not extend far along it. In 
Ophioglossum the transverse section of the stock shows an interrupted 
ring of xylem-bands, the interruptions representing the closely grouped 
and overlapping leaf-gaps, as will be readily understood by comparison 
of Fig. 236, Nos. 4, 5. But in simple cases, and especially near to the 
base of the stock, the ring may appear more complete (Fig. 258). The 
development is endarch, and there is no process of secondary thickening 
except that a few tracheides may occasionally be added peripherally to 
those primarily formed. In the root also there may be a feeble formation 
of secondary wood, especially in the neighbourhood of the insertion of 
an adventitious bud (Boodle).' In He/minthostachys the vascular ring is 
interrupted only on the oblique upper side, by the leaf-gaps. The xylem 
is, however, mesarch, while the secondary thickening is altogether absent 
(Farmer and Freeman). 
