LEAF IN THE VASCULAR CRYPTOGAMS AND GYMNOSPERMS. 
575 
formation of wings, still in the arrangement of the cells in the young leaf, and in their 
subdivisions, there are points in common with Marsilia. 
Osmundacea:. 
I. —Osmunda regalis, L. 
The young phyllopodium, before any pinnse are formed, consists of an elongated basal 
portion with massive lateral wings, and a less distinctly winged apical portion, which 
is terminated by a bluntly conical, and comparatively massive apex : the whole is 
covered by numerous mucilaginous hairs. On removing the extreme apex by a 
transverse cut, and treating with suitable reagents, it is found that the apex is 
occupied by a tliree-sided, conical, apical cell, which is so situated that one side faces 
the apex of the stem, while the opposite angle is directed away from the apex of the 
stem, that is towards the dorsal side of the leaf (Plate 37, fig. 4). From this cell 
segments are cut olf parallel to the three sides, in regular left-handed spiral* 
succession, as at the apex of the stem of Equisetum. The segments are further 
divided up fundamentally on the same plan as laid down by Cramer for Equisetum, 
and shown in the well-known figures copied in Sach’s Text Book. Irregularities of 
arrangement of the walls are however to be found, as shown in the lower left-hand 
corner of fig. 4, on Plate 3 7. The apical cell remains clearly marked even after the first 
pinnae have appeared : for instance, it was still to be seen at the apex of a leaf, which 
had already formed six pinnae (Plate 37, fig. 5); but in one which had formed twelve 
pinnae no apical cell was to be seen, while in the latter case the whole bulk of the 
conical apex was much smaller than in leaves at an earlier stage. After the three- 
sided apical cell has lost its identity, and the whole apex of the leaf has been 
reduced in bulk as above described, a marginal series of cells similar to, though less 
marked than in the case of other Ferns, is found extending over the apex of the leaf; 
but it has not been possible to recognise among the cells of this series any single 
cell acting the part of a two-sided apical cell. 
The pi nine are formed monopodially, and in strictly acropetal order on the 
phyllopodium: as in many Ferns, their insertion is not perfectly lateral, but towards 
the ventral face of the leaf, and along the lines of the more or less developed wings. 
The pinnules also appear in acropetal order, and are developed monopodially on the 
pinnte. I have not seen any case of dichotomous branching in the leaf of Osmunda 
regalis, such as is described by Sadebeck, Prantl, and others as occurring in the 
leaf-branchings of higher order in many Leptosporangiate Ferns. It has been 
ascertained in the case of certain other Ferns that there is a distinct genetical relation 
between the pinnae and the segments of the apical cell, though that relation is not 
* i.e., left-handed in the mechanical sense : the succession was left-handed in all the cases observed. 
