Osmunda claytoniana , Z., and O . cinnamomea , Z. 83 
3. A single two-sided apical cell is early established which 
gives place to a single nearly square one, and ultimately to a 
row of marginal initials. No cases were observed where mar- 
ginal growth was at once established. 
3. The prothallium is traversed by a thickened midrib of 
nearly uniform diameter in O. cinnamomea , but broader in 
front in O. claytoniana. 
4. Branching of the young prothallium is especially marked 
in O. claytoniana. Adventitious prothallia are formed later in 
both species, but especially in O. cinnamomea. 
5. The chloroplasts are sometimes of extraordinary size in 
O. cinnamomea. 
6. The antheridia differ in structure from those of other ferns. 
They approach most nearly those of the Hymenophyllaceae 
and Gleicheniaceae. The spermatozoids resemble most nearly 
those of Equisetum. They arise by direct transformation of 
the nucleus. The cilia and vesicle are of cytoplasmic origin. 
7. The archegonium sometimes has the neck-canal-cell 
divided. Little or no starch is present in the canal-cells or 
the egg. A polar body, distinct from the ventral canal-cell, 
may be present. 
8. Several spermatozoids usually penetrate to the central 
cell of the archegonium, but only one enters the egg, which 
then secretes a wall that prevents the entrance of others. 
9. The first division in the embryo is parallel with the axis 
of the archegonium, as is also the second ; but the position of 
the quadrants with respect to the prothallium is the same as 
in the other ferns. 
10. The primary organs are determined by the formation 
of the quadrant walls. Leaf and stem arise from the epi- 
basal half of the embryo ; root and foot from the hypo- 
basal. 
11. Stem, leaf, and root grow from a tetrahedral apical cell, 
which is one of the original octants of the embryo. 
13. The foot is very large, and the embryo for a long time 
dependent upon the prothallium. The calyptra is also large, 
and these points, together with the late differentiation of the 
G 3 
