578 
MR. F. O. BOWER ON THE COMPARATIVE MORPHOLOGY OF THE 
in Osmunda, there is on each side a massive winged development, which owes its 
origin to an activity of growth and division of the peripheral cells, including those at 
the surface. At first this development is, as in Osmunda regalis and cinnamomea, 
restricted to the lateral margins, and as in those plants, no doubt homologous with the 
basal winged development in other Ferns so often referred to (Plate 37, fig. 8, a, b). 
Later, however, the activity of growth and cell-division extends transversely across 
the face of the phyllopodium, and the result is a continuity of the transverse portion 
of the sheath with the lateral wings (Plate 37, fig. 8, c). In the mature leaf this may 
be clearly seen with the naked eye. This continuation of the winged structure across 
the face of the phyllopodium is comparable with that resulting in the so-called “ axil¬ 
lary stipule,” or with that which produces the familiar orbicular leaves, for example 
in Tropceolum, Hydrocharis, &c. (Goebel, Verlg. Entw., pp. 232-4). Tins case of 
Todea has an important bearing upon similar structures in Angiopteris, Stangeria, and 
Ceratozamia. 
Todea superba appears to have no scale-leaves, with abortive apices, as in Osmunda, 
but in Todea barbara scale-leaves may be found in considerable numbers. 
Comparing the development of the leaf in the Osmundaceoe, as shown in the above 
examples, with that of other Leptosporangiate Ferns, it is clear that an advance has 
been made in robustness of character of the phyllopodium, and therefore in its adaptation 
to serve as a supporting organ. As I have above pointed out, the growth with a two- 
sided apical cell, from the segments of wdiich two marginal series of cells are derived, 
is to be looked upon in the case of the Fern leaf as a reminiscence of a development 
as a flattened expansion. This flattened expansion, by habitual thickening of the 
central portion, and frequently by corresponding reduction of the lateral wings, 
especially in the lower parts of the leaf, may be regarded as having given rise to 
structures such as the leaves of most Ferns. In the Osmundacece, though the winged 
character is not lost, the development of the apex of the leaf is of a massive and solid 
character from the first, and continues so as long as the apical cell persists ; it is a 
structure developed from the first, not in two, but in three dimensions of space. It 
has been clearly shown by the observations of Treub on the apex of the stem of 
Selaginella Martensii* that there is in that plant sometimes a two-sided, sometimes a 
three-sided apical cell, and that intermediate forms may be found between them : it 
might therefore be concluded that no great importance is necessarily to be attached to 
a difference in that respect. But in this case of the leaf in the Leptosporangiate 
Ferns the change from a two-sided to a three-sided cell is accompanied by changes of 
other characters, such as a more massive apex of the young leaf, the absence of 
marginal series of cells in the lower parts of the phyllopodium and pinnae, as well as 
differences of internal structure, and in the reproductive organs. On these grounds 
it appears justifiable to attach more importance to this transition from the two-sided 
to the three-sided apical cell, than is necessarily implied by such a change. The leaf 
* Rcclierclies sur les organes de la vegetation du Selaginella Martensii. Spring. Leide, 1877. 
