meristems of Ferns as a Phylogenetic Study. 353 
a definite marginal series as a very natural concomitant of 
the more complex construction of the apex of this leaf. 
The base of the phyllopodium of Osmunda is considerably 
enlarged, so as to form a wide sheath, and the wings are here 
laterally extended : in the young leaf their margins are 
bluntly rounded, but later they run out into thin and mem- 
branous lateral flaps, consisting in part of but a single layer 
of cells : none the less are these to be recognised as develop- 
ments of the wings, and a comparison may fairly be drawn 
between this thinning out of the wings, and that which is 
found in the upper parts of the leaves of Todea superb a and 
hymenophyltoides , and lends to them that ‘ filmy 5 character 
which will be discussed later. Above the sheath the phyllo- 
podium of Osmunda is almost cylindrical, the wings being 
reduced (as in the petioles of the higher vascular plants), 
while in the upper part of the leaf, and especially the pinnae 
and pinnules, they are more extended. The leaf of Osmunda 
is thus winged throughout, but shows in its lower portion 
varieties of development which might be compared with such 
as are seen among the higher plants. 
But it is in Todea barbara that the structure of the young- 
wings, and the nature of the segmentations of the margins 
have been most carefully examined. I have already described 
the base of the leaf of Todea superba 1 , and that of T. barbara 
is similar to it. In early stages of development the base of 
the leaf resembles that of Osmunda , being furnished with 
massive wings: later the activity of growth extends trans- 
versely across the face of the phyllopodium, resulting in such 
a development as may be compared to the axillary stipule 
which is not uncommon among Angiosperms, and also finds 
its homologue in the commissure of the Marattiaceae and 
in Stangeria. Here also the margins, which are at first blunt 
and rounded, extend as the leaf develops into membranous 
flaps, which consist at their extreme edge of only one layer 
of cells. The conformation of the upper parts is generally 
1 Phil. Trans., 1884, p. 578, Plate 37, Figs. 8 a, b, c. 
