Boodle . — Anatomy of the Gleicheniaceae. 727 
xylem, is C-shaped, and divides into three separate arched 
bundles, probably without much previous buckling. 
In G.flabellata there is greater complexity. The behaviour 
of the xylem could not well be made clear without the aid of 
diagrams, so the description will be restricted to the bundle, 
as limited by the endodermis. Near the top of the petiole the 
bundle becomes elongated at right angles to its median plane, 
so as to form a low arch with the ends turned in like a com- 
pressed C. The ends approach until they meet, when the 
endodermis becomes fused, so that the bundle now has a com- 
plete inner and outer ring of endodermis. The form of the 
bundle is now a long hollow ellipse. Two bridges of bundle- 
tissue are now formed across the central cavity, and the bundle 
becomes a chain of three loops. By splitting of the bundle 
through the two bridges, three closed annular bundles are 
produced, of which the middle one, belonging to the rachis, 
has an annular xylem. Before long all three bundles open 
and return to the typical arched form. In G. dichotoma the 
division of the bundle takes place in a somewhat similar 
manner. 
There is the same transition to collateral structure that 
is found in the leaf of many other Ferns. In G. flabellata 
one of the secondary prinnae not very far from its tip had 
a bundle with an oval endodermis (not invaginated) and an 
arched xylem with three protoxylems. The form of the 
xylem is very similar to that found by Gwynne-Vaughan 
(’01, PL III, Fig. 8) near the tip of the rachis in Loxsoma. 
The phloem curves round the hooked ends of the xylem, so as 
nearly to meet ; the bundle is therefore practically concentric. 
In the pinnules, however, the bundle of the midrib is reduced 
to collateral structure. The small bundle, which is circular in 
outline, is bounded by an endodermis, has a roughly semi- 
circular group of xylem, with a layer of phloem on its curved 
lower side, and one protoxylem-group at the middle point 
of its flat upper side. This again corresponds with what is 
found in the principal vein of the leaf-segment of Loxsoma 
(Gwynne-Vaughan, ’01, PL III, Fig. 7, e). 
