4 2 Lang . — Prothalli of Ophioglossum pendulum 
the account of the mature plant, and show in what particulars 
differences exist between them. 
The general plan of construction of the roots of the young 
plant is similar to that of those springing from old rhizomes. 
As in these, root-hairs are absent, the outer walls of the 
superficial cells being at most bulged outwards to form short 
papillae. There is a broad parenchymatous cortex, in a 
middle zone of which an endophytic Fungus is present in the 
first two or three roots (Fig. 63). This appears to constitute 
a mycorhiza, as is the case with all the roots in some other 
Ophioglossaceae. The stele is surrounded by an endodermis 
with corky radial walls ; within this comes a single layer of 
pericycle. The stele of the first root (Fig. 64) is constantly 
triarch. The three groups of xylem, with which the small 
phloem-groups alternate, usually surround a small pith, though 
they are sometimes joined together. The second root is 
similar, but the stele is tetrarch (Fig. 63). The same holds 
for succeeding roots which show a gradual increase in thick- 
ness ; the fourth root had its cortex free from Fungus and 
densely filled with starch, like the roots of the mature plant. 
The internode below the first leaf varies in length and 
thickness in different individuals. The single stele also 
presents slight differences, though the general plan of con- 
struction is constant. It is limited on the outside (Figs. 65, 66) 
by a well-characterized endodermis, within which come one or 
two layers of fairly large clear cells, constituting the pericycle. 
The phloem, which consists of narrow elements, surrounds the 
xylem. The xylem is in some cases a solid central strand, 
but more usually a few parenchymatous cells are present in it. 
These are often conspicuous in the centre, constituting a more 
or less distinct pith (Figs. 64, 65). Just below the origin of 
the first leaf-trace the pith, if present, increases in size, and is 
continuous with the parenchyma intervening between the 
xylem of the departing leaf-trace and that of the stele. If the 
stele is solid in the lower part of the internode parenchyma 
appears in the centre of the xylem in preparation for the 
departure of the trace. As a rule the stele after, a leaf-trace 
