714 Boodle . — Anatomy of the Gleicheniaceae. 
in G. (. Mertensia ) dichotoma the form of the bundle is as in 
Eugleichenia. In the latter species the internal structure of 
the bundle might be regarded as giving evidence of derivation 
from the usual type for Merteivsia. 
G. dicarpa may be taken to illustrate the type of petiolar 
structure found in Eugleichenia . Fig. 7 is a transverse 
section of the bundle. The xylem has the form of an arch 
with incurved ends, and possesses three protoxylem-groups. 
The position of the latter is indicated by the three cells 
marked cp. in the drawing, which are elements resembling 
cavity-parenchyma. There is a protoxylem-group consisting 
of annular and spiral tracheides (some of which are often 
crushed) in contact with the outer side of each of these 
cells, i. e. radially external to them. It is thus seen that the 
xylem agrees with that of Anemia Phyllitidis , in that three 
protoxylems are present, and are internal to the xylem-arch, 
one being median, and the other two in the concavity of the 
hooked ends of the xylem. The phloem in G. dicarpa clothes 
the external surface of the xylem-arch, and bends inwards 
round its ends, following its outline, and continuing upwards 
towards the top of the arch, e.g. about three-quarters of the 
way. The phloem has the same constituent elements as in 
the stem, but has fibrous elements in addition. The proto- 
phloem, forming the boundary of the phloem towards the 
pericycle, can be recognized by its small elements (pph\). 
The latter are fairly thick-walled, but have not been repre- 
sented so in the drawing, in order that the phloem-fibres 
might be distinguished by this character. The phloem- 
fibres are seen at f, /., and at the two corresponding points 
in the other half of the bundle. They have been formed by 
thickening and lignification of the walls of phloem-elements ; 
both sieve-tubes as described by Poirault (’ 93 , p. 195) for 
G . circinata and G. dicarpa , and also phloem-parenchyma, 
being thus transformed. A few similar fibres may occur 
in the phloem outside the top of the xylem-arch. The 
central region of the bundle probably represents pericycle, 
and consists partly of parenchyma and partly of sclerotic 
