710 Boodle.— -Anatomy of the Gleicheniaceae . 
distance below the periphery of the xylem, the remainder 
of the tracheides being scalariform. In Fig. 2 about fourteen 
protoxylems are present ; some of these may be recognized 
as groups of small darkly stained elements (px.). Fig. 3 
contains a peripheral piece of the xylem of G. dichotoma , 
showing the scalariform tracheides separated by xylem- 
parenchyma (xp.). Fig. 4 represents one of the lobes of the 
xylem of G. circinata , and shows the mesarch position of 
the protoxylem (px.). Part of a young stele of G. dichotoma 
in Fig. 6 is at the stage in which the protoxylem (px.) is the 
only part of the xylem differentiated ; young tracheides (t., t), 
which have not yet begun to thicken their walls, are seen on 
the outer side of the protoxylem. Fig. 5 is a radial section 
of the outer part of the stele of G. circinata showing the 
protoxylem (px.) with one scalariform tracheide on the outer 
side ; pph. is a protophloem element. Fig. 14 may be referred 
to for the relation of the protoxylem-groups to the lobes of 
the xylem in G. dichotoma. In species where the xylem is 
lobed, there is nearly always a protoxylem immersed in or 
below the xylem of each lobe, though there may sometimes 
be additional protoxylem-groups having no corresponding 
prominences. 
In the internode of G. dichotoma the xylem generally shows 
six prominences with six protoxylems. The lobes are fairly 
symmetrically placed, so that the xylem may be described 
as roughly hexagonal, with rounded angles (Fig. 14). The 
three lobes on the lower half of the xylem serve for the 
attachment of, roots, though a root is occasionally inserted 
on one of the upper lateral lobes, while the three protoxylems 
in the upper half are connected with leaf-traces. A rhizome 
of G. dichotoma^ var. nervosa , which was larger than that of the 
type, had a xylem with 8-9 lobes. In G. circinata there are 
often six as in G. dichotoma. 
In these species the xylem usually has a nearly symmetrical 
form, with protoxylem-groups equal in number to the lobes. 
In G. dicarpa , on the other hand, there are often 7-8 proto- 
xylems, of which 2-3 on the upper side have no distinct 
