86 Campbell . — On the Prothallium and Embryo of 
here. As the root of Equisetum also has this form of apical 
cell, it seems probable, as Bower 1 suggests, that this is the 
primitive form from which the single four-sided cell found 
in the later roots of the species of Osmunda under considera- 
tion, and the group of initial cells in the roots of the Marat- 
tiaceae, have been derived. It would be interesting to know 
whether in the first root of the embryo of the latter, anything 
approaching a single apical cell of the ordinary type is to be 
found. 
The points of resemblance between the Osmundaceae and 
so many other groups, shown especially in O. claytoniana , 
indicate that we have to do with a primitive, undifferentiated 
group, standing near the junction of several others. Next to 
them, and probably connecting them with the Bryophytes, 
are the Ophioglosseae, with Ophioglossum as the most primitive 
form. Through Botrychium, Ophioglossum is connected directly 
to the Osmundaceae, and through them to the whole lepto- 
sporangiate group of ferns. 
The position of the Marattiaceae is difficult to determine 
on account of our imperfect knowledge of the embryo, and 
almost complete ignorance of both prothallium and embryo 
in the Ophioglosseae. While showing some resemblances to 
the Osmundaceae, I am rather inclined to look for an origin 
of the group lower down, perhaps directly from the Ophio- 
glosseae, although the structure of the later roots of the 
Osmundaceae does show points of resemblance to the Marat- 
tiaceae, and the absence of a midrib in the prothallium of the 
latter recalls the prothallium of the higher Leptosporangiatae. 
As the living Marattiaceae, however, are but a remnant of 
a once predominant group, it is not safe to assume that the 
prothallium of the living forms represents necessarily its 
primitive character. It may perhaps bear the same relation 
to the primitive forms that the prothallium of say an Aspidium 
does to hat of Osmunda. 
The Equisetineae have usually been regarded as holding 
a position entirely apart from the other Pteridophytes, but 
1 Bower, Meristems of Ferns, p. 318. 
