some Species of Gleichenia . 
423 
Comparison with other Species. 
In the species of Gleichenia examined two types of nodal island may 
be distinguished. In G. pectinata 3 G. flabellata , and G. linearis , Clarke, 1 
which belong to the subgenus Mertensia , the first stage in the formation of 
a nodal island is an increase in the number of cells of xylem-parenchyma 
near a protoxylem-group, as described above for G. pectinata. As this 
nodal island increases in size (i. e. when traced acropetally), it becomes 
associated with the neighbouring protoxylem-groups. Since the extended 
nodal island thus constituted forms the inner limit of the leaf-trace, the 
latter has endarch structure when it separates from the stele. The other 
type of nodal structure is shown by G. dicarpa , G. rupestris , R.Br., and 
G. circinnata , with its variety semivestita , belonging to the subgenus Euglei- 
chenia. Here the nodal island does not originate in connexion with a proto- 
xylem-group, and the xylem of the leaf-trace separateswith one or more of 
the protoxylems mesarch (cf. Boodle, ’ 01 , Plate XXXIX, Fig. 22). 
A very young node of G. circinnata var. semivestita will now be 
described, and will furnish an example of the second type of nodal island. 
The node was at a distance of about 1 cm. from the growing apex. The 
structure of the stem showed signs of dorsiventrality at an early stage ; near 
the growing point the three lower protoxylems became lignified before the 
two upper groups, and soon gave off root-traces. Text-fig. 1 1 shows the 
structure of the stem below the node ; 1, 2, and 3, are the lower protoxylems ; 
4 a and 4 b (derived from the branching of 4) and 5 are the upper groups. 
4 b again branches to form 4 b r and 4 b", and at the same time a nodal mass 
of parenchyma is differentiated (Text-fig. 1 2, n.i .), and is easily distinguish- 
able from the surrounding immature tissue, which is destined to form 
normal xylem. The nodal mass of parenchyma is not immediately associ- 
ated with a protoxylem-group, but is equidistant from the protoxylems 
4 b', 4 b" , and 5. It increases in size (when followed acropetally), and soon 
contains some phloem-elements. A new protoxylem-group (6 in Text- 
fig. 1 3) then arises, and has no connexion with any of the other proto- 
xylems. Text-fig. 2 1 shows the lowest section of this protoxylem, the 
end-wall of the single trachea being seen in surface-view. In the transverse 
section this trachea was separated by a long distance from any other ligni- 
fied element. It was itself very feebly lignified, but showed distinct 
sub-scalariform markings.. Text-figs. 2 2 and 2 3 are from higher sections, 
two protoxylem-elements being present in Fig. 2 3. 
To return to the general description of this node, in the next stage 
after that shown in Text-fig. 1 3, the xylem becomes cut across between the 
protoxylems 5 and 6, and between 4 a and 4 b\ the endodermis insinuating 
1 This species was referred to under the name of G. dichotoma in ‘ Anatomy of Gleicheniaceae ’ 
(Boodle, ’01). 
Gg 
