540 FILICALES 
structure certain fossils attributed to the Botryopterideae have pronounced 
Osmundaceous characters: in view of the sequence of fossils above quoted, 
it seems probable that the Osmundaceous structure is referable in origin, 
with upward differentiation of the stele, to some type of the nature of the 
Botryopterideae (Kidston and Gwynne-Vaughan). It thus appears that a 
study of the related fossils in their stratigraphical sequence lends no serious 
support to a theory of reduction of the stele from an “ amphiphloic siphono- 
stele”: it indicates rather an upward development from a protostelic state. 
Taken with the comparative considerations already advanced, the evidence 
against Jeffrey’s view appears very strong indeed. 
Zenetti! had already regarded the stele of Osmunda as being in the 
up-grade of development, and had compared it with the structure seen in 
certain of the Lycopodiales. With these a very interesting parallel may 
be drawn, and especially with that series illustrating a progressive elaboration 
of the stele, and its disruption into separate strands, which Kidston has 
recently demonstrated by a stratigraphical sequence of fossils as cogent as 
this in the Osmundaceae (see above, pp. 230, 337). The fact that such 
parallels have been shown to exist in distinct phyla is in itself a support of 
the views above indicated. 
EMBRYOLOGY. 
The primary embryology of the Osmundaceae being on the same 
plan as that of the Leptosporangiate Ferns as a whole, it need not be 
described in detail. The Leptosporangiates all differ from the Marattiaceae 
in the position of the basal wall: in the latter it is transverse to the axis 
of the archegonium, in the former it.is parallel with it: in relation to this 
the epibasal half, which gives origin to the axis and leaf, is here directed 
laterally, and the cotyledon originates from its lower quadrant. The 
consequence is that, ae in all the other Leptosporangiates, the cotyledon 
of the Osmundaceae emerges on the lower side of the prothallus, not from 
the upper as in the Marattiaceae. Comparing the embryo itself with that 
of other Leptosporangiate Ferns, it will suffice to remark that. in the 
segmentation there is somewhat less regularity in the later divisons, and 
that the external differentiation of the members appears later, the embryo 
retaining longer than in them its spherical form. These are but minor 
differences; they indicate, however, for the Osmundaceae an intermediate 
place between the typical Leptosporangiates and the Eusporangiate Ferns.” 
A similar intermediate character comes out also from comparison of 
the meristems of the Osmundaceae with those of the Marattiaceae on the 
one hand, and of the typical Leptosporangiate Ferns on the other. I 
have shown at length elsewhere,’ that in respect of the apices of root, stem, 
1 Bot. Zeit., 1895, pp. 72-76. 2 For details see Campbell, Mosses and Ferns, p. 356. 
3 Quart. Journ. Micr. Sci., vol. xxv., 1885, p. 75, etc. ; Phil. Trans., 1884, part ii, p. 
565; Ann. of Bot., vol. iii., p. 305. This matter will be taken up ‘again later, when 
the general comparison of Ferns is made, and also in Part iii. 
