Anatomy of the Ophioglossaceae. /. 
21 I 
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external endodermis left by the departure of the leaf-trace. The condition 
is thus much as in the adult region, except that the endodermis is con- 
tinued much more deeply into the pith. At no level, however, is the 
internal endodermis complete. When the external endodermis forms 
a complete ring, and before the gap in 
the xylem closes, the endodermal mark- 
ings within the stele cease. The next 
leaf-trace is much larger, its departure 
follows the adult type, and the leaf-gap 
is short. The stele has now become 
wider and the zone of xylem thicker, 
with indications of secondary growth. 
This plant thus shows an imperfect 
internal endodermis associated with one 
extended leaf-trace departure. 
Plant D may be described very 
briefly, since, as Text-fig. 6 will show, 
it only differs in one essential point from 
the preceding plant. Here also the first 
leaf-traces are small and the endodermal 
relations at the leaf-gap conform to the 
adult type. The interest of this plant 
lies in the slow departure and the long 
leaf-gap left by the third leaf-trace. 
This constitutes the specialized inter- 
mediate region. After the xylem of the 
third leaf-trace has separated from the 
rest of the xylem, but before any inter- 
ruption of the external endodermis, en- 
dodermal markings appear on the radial 
walls of cells within the arms of the 
horseshoe-shaped xylem of the stem. 
This internal endodermis is at first quite 
unconnected with the external endo- 
dermis. As the leaf-trace separates and 
the external endodermis is interrupted, 
these bands of internal endodermis be- 
come continuous with the free ends of 
the gap in the outer endodermis. This then appears to extend deeply 
into the pith, lining the tube of xylem, but not forming a complete 
internal endodermis. The condition is thus the same as in the long leaf- 
gap of the preceding plant. On passing further up the gap in plant D, 
however, the internal endodermis does become complete for some distance. 
Text-fig. 6. Reconstruction of the stele 
of plant D. Description in text. 
