82 Campbell — On the Prothallium and Embryo of 
these was very much in advance of the other, and it is 
probable that the larger one would have ultimately starved 
out the other. 
Comparison with the Embryo of other Pteridophytes. — Com- 
paring the embryo of Osmunda with that of other Pteri- 
dophytes, it seems to approximate most nearly, as might 
have been expected, that of the Polypodiaceae, but differs in 
several particulars from them, i.e. the very large foot, the 
position of the quadrants with reference to the archegonium ; 
the greater irregularity in the divisions of the quadrants ; the 
small size of the apical cell of the root and the greater size 
of the root itself; and the imperfect differentiation of the 
primary tissues. In all these respects it departs furthest from 
the Marsiliaceae, the most specialized of the Leptosporan- 
giatae, and probably approaches the Ophioglosseae ; but as 
the embryology of the Ophioglosseae is entirely unknown, and 
that of the Marattiaceae almost equally so, a comparison with 
these is at present impossible. The Gleicheniaceae, to judge 
from Rauwenhoff’s 1 2 3 imperfect account of the embryo, are 
nearer the Polypodiaceae than the Osmundaceae in this 
respect. With Equisetum 2 and Isoetes 3 there is little in 
common beyond the first divisions of the embryo. 
Summary and Conclusion. 
The principal points brought out in the foregoing pages 
may be summarized as follows : — 
i. The spores of Osmunda claytoniana and O.cinnamomea 
germinate immediately and may form a protonema as in the 
Polypodiaceae, this being especially noticeable in the former 
species, where the formation of a cell-surface at once is un- 
usual ; or a cell-surface, or even a cell-mass, may be the first 
product of germination. 
1 L. c. p. 52. 
2 See Sadebeck, ‘ Die Gefasscryptogamen ; ’ in Schenk’s Handbuch. 
3 Campbell, Contributions to the Life-history of Isoetes; Annals of Botany, 
Vol. V. no. xx. 
