mer is terns of Ferns as a Phylogenetic Study. 339 
Comparison of Apices of Leaves. 
If we pass in general review the characters of the apex of 
the leaf in the series of Ferns above described, as we proceed 
from the Hymenophyllaceae to the Marattiaceae, an advance 
in complexity of structure is to be seen similar to that already 
noted in root and stem ; but it is even more marked here, 
since in the simpler forms the two-sided apical cell is con- 
stantly found. The following general conclusions result 
from a comparison of the apical meristems of leaves in the 
Filicineous series : — 
(1) That the apex itself is more bulky, and its curvature 
necessarily less sharp in the Marattiaceae than in the Osmun- 
daceae : while a similar relation holds between the Osmun- 
daceae and the leptosporangiate Ferns. 
(2) That in the leptosporangiate Ferns a two-sided apical 
cell with regular segments is the type for the leaf : that 
(as occasionally happens as an irregularity in young leaves of 
the Polypodiaceae) a three-sided apical cell, with three rows 
of segments is the rule for Osmundaceae : that in Marattia 
also this is often the case (though not always), but the growth 
of the segments is much greater in proportion to that of the 
apical cell than in Osmunda : that what is the exception 
in Marattia is the rule in Angiopteris , viz. that the apex is 
occupied not by one initial cell, but by a number, apparently 
three. 
(3) That therefore, in respect of the structure of the apex 
of the leaf, the leptosporangiate Ferns, Osmundaceae and 
Marattiaceae form a natural and gradual series of which 
the first are the simplest and the last the most complex. 
(4) That on rising through this series of Ferns the apical 
cells are proportionately narrower and deeper, while in the 
highest terms of the series the initial cells are often oblong 
with square base : thus there is a lowering of the centre of 
construction as we rise in the series. 
(5) These results correspond to those already acquired 
A a 
