532 FILICALES 
flattened expansion: and developmentally it is found that this arises by 
transverse growth of the superficial tissues, especially at the wings them- 
selves. The result in Osmunda is a mere flattened leaf-base; but in Zodea 
superba the development extends also as a 
transverse commissure across the adaxial 
face of the leaf-stalk. This development, 
so exceptional in Ferns, may be compared 
with the stipular development in the 
Marattiaceae, which is also extended as 
a commissure across the leaf-stalk. The 
two cases, though differing in detail, appear 
alike in morphological nature. 
The sporangia of Zodea are borne 
only on the under surface of the leaves, 
but in Osrnunda they are inserted in- 
differently on both sides of the much- 
contracted part, so that at maturity it 
appears to be completely covered by them. 
There is no protective indusium. The 
sporangia themselves are relatively large, 
of pear-like form, and thick-stalked. They 
consist at maturity of a single layer of 
cells forming the wall, but with a few 
tabular cells within: a group of polygonal, 
thick-walled cells in a lateral position, 
but nearer the distal end, is recognised 
as the annulus: it is related to the slit 
of dehiscence so that the latter passes 
from the centre of the annulus, over the 
distal end, and approaches the © stalk 
on the opposite side of the sporangium 
(Fig. 294). The line of dehiscence, de- 
fined structurally by narrow thin-walled 
cells, gapes widely at ripeness ; _ this 
arrangement requires elbow-room, which 
Fic. 294. 
Todea barbara, Moore. Sporangium. the lax arrangement of the sporangia 
A, in side view, closed. 8B seen from os * . wy a zi 
behind. C from in front, in both cases after readily allows. Those sporang1a which 
dehiscence ; the annulus is darkly shaded. are in near proximity to one another 
*8o. (After Luerssen.) hoe i : 
originate simultaneously: there is no 
interpolation, nor any marked sequence of their origin. Nor is there 
any regularity in their orientation: in Osmunda the sporangia face in 
the most various directions: and even in Zodea, where their arrangement 
has some reference to the nerves of the leaf, the sporangia upon a 
single nerve show no common rule of orientation. These Ferns are thus 
non-soral, 
