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Harriet E. Allison. 
been formed, the foliage-leaves arise, probably forming a pro¬ 
tection for the younger leaves. As the apex of the fern continues 
to grow, the nest leaves die down, forming a great mass of humus 
and a number of foliage-leaves succeed them and so on. It is thus 
seen that the rhizome shows on the dorsal surface two rows of 
leaves, with a set of nest-leaves alternating with a set of foliage- 
leaves. On the ventral surface of the rhizome there is a thick 
covering of dark wiry rootlets. 
This species, which is conspicuous in the genus for its large 
size, shows a corresponding complexity of internal structure. The 
actual rhizome, the structure of which is about to be described, 
was one of medium size, measuring about ^ inch in diameter. 
Serial sections were cut through the insertion of three leaf bases, 
two of the leaves being foliage-leaves and the other a nest-leaf. 
The nest-leaf corresponds in essentials to the other leaves, the 
anatomy and insertion of the leaf being almost similar to that of 
the foliage-leaves. The form of the nest-leaf would thus appear 
to be an adaptation to habit, and it seems probable that the nest- 
leaf and the foliage-leaf originated from a common type. 
In transverse section, the anatomy of the rhizome is seen to 
be somewhat complex. The meristeles are very numerous, and 
are scattered over the transverse section. Moreover, the close 
insertion of the leaves upon the axis adds to the complication. It 
is possible, however, to identify an outer ring of meristeles, forming 
a dictyostele. These meristeles are seen in the serial sections to 
unite frequently with one another, and as frequently to divide, so 
that they form a vascular network. The meshes of this net are 
not leaf-gaps, but are of the nature of stelar “ perforations.” 
Internal to the perforated dictyostele is a large number of 
medullary strands, which are formed either by division from the 
meristeles of the primitive dictyostele, or from already existing 
medullary strands. On the ventral or lower surface, rootlets are 
given off from the dictyostele as in other species. The whole 
ground-mass of the rhizome consists of cells with thickened mem¬ 
branes. The meristeles are each surrounded by a sheath of two 
or three rows of cells with thickly lignified walls. The structure 
of the meristele is quite normal, and there is no marked protoxylem 
distinguishable. At the centre is a core of xylem, composed of 
tracheids with one or two parenchymatous cells, surrounded by a ring 
of phloem, and by a pericycle two or three cells deep. An endodermis 
is present, but owing to the hardness of the sheath, it was often 
crushed or ruptured in cutting. 
