572 
ME. F. 0. BOWER ON" THE COMPARATIVE MORPHOLOGY OF THE 
while in other cases the winging is less marked, but still traceable (Trichomanes 
Prieurii). I have not found any marked modification of contour at the base of the 
leaf in this family, and this coincides with the observations of Prantl.* 
This author describes the young leaf of Trichomanes speciosum ( l.c ., p. 6) as having a 
two-sided apical cell, from which two longitudinal series of segments are cut off by 
converging walls. These segments divide by longitudinal walls, so as to form two 
series of cells, occupying the margins of the leaf (marginal series), and internal cells 
forming the central part of the leaf (compare Prantl’s fig. 2, Taf. 1). Thus the 
phyllopodium is from the first, at least, potentially a flattened structure, which, by 
increase in bulk of the tissues derived from the internal cells and by continued 
growth at the margins, becomes a winged structure ; the marginal series of cells 
are in a corresponding position to those which have been shown to be so intimately 
connected with the winged development in the leaves of other Ferns. As to the 
branching of the phyllopodium, it has been shown by Prantl to be distinctly 
dichotomous, at least in the upper portions of the leaf; the upper part of the 
phyllopodium is thus a sympodial development. Further, it is clear that, the 
tissues of the leaf thus originating in the first place from a two-sided apical cell, 
and then from growth and repeated division of marginal series, of cells, are really 
the outcome of a development referable to a single plane, that is in two dimen¬ 
sions of space only. 
Passing on to Ceratopteris thalictroides ,+ in which the development of the leaf has 
been so accurately followed by Kny, the apex of the young leaf is here also occupied 
by a two-sided apical cell, from which two series of segments are cut off; these 
segments divide, as in Trichomanes, in such a manner that a series of cells is formed 
running along each margin of the flattened leaf, and continuous to its base (compare 
Ivny’s figs., Taf. 6) ; this character remains in the permanently angular cross-section 
of the lower part of the phyllopodium. Thus the leaf of Ceratopteris is also potentially 
a flat structure, which assumes a winged character by increase in bulk of the central 
part, and continued growth at the margins. The identity of the apical cell is subse¬ 
quently lost, the apex of the leaf being then occupied by a continuation of the 
marginal series. The first pinnae arise monopodially in acropetal order, and first 
appear as marginal outgrowths, but with no distinct reference to the segments of the 
apical cell. The structures which Kny calls stipular scales (stipular-schuppen), have a 
similar structure to the perulse (spren-schuppen), and except in their position do not 
seem to me to be of a stipular nature. 
The type of leaf-development seen in Ceratopteris prevails in its main characters 
also in other Ferns which have been investigated: e.g., species of Asplenium,\ in 
* Unters. z. Morph, d. Gefasskiypt. Heft I. Leipzig, 1875. 
f Kny, Hie Entw. d. Parkeriaceen. Dresden, 1875. 
X Sadebeck, Zur Waclistkumsges. d. Farrnwedels. Verk. d. bot. Ver. Brandenburg. Bd. 15 (1873), 
p 123. 
