8o Campbell . — On the Prothallium and Embryo of 
of the plerome are not nearly so well marked as in most ferns, 
and a distinct bundle-sheath is not present. At first all the 
cells of the plerome contain protoplasm and a distinct nucleus, 
but later the tracheids, as usual, lose their protoplasmic 
contents. There are usually two groups of tracheids formed, 
and from these points, as usual, the formation of others proceeds 
toward the centre of the bundle. The rest of the bundle is 
composed of nearly similar elongated cells, but no true sieve- 
tubes were noted. 
The root-cap is not as regularly stratified as in the Poly- 
pod iaceae, and in this also Osmunda comes nearer Botrychium. 
It was not examined in the full-grown root, but probably, 
as in the mature plant, it is derived in part from the lateral 
segments of the apical cell. 
A comparison of the first root of the two species shows no 
very noticeable differences. The divisions are perhaps a little 
more regular in O. claytoniana , and the segments rather 
smaller as compared with the apical cell ; and the divisions in 
the young segments seemed to be rather more rapid, so that 
it approaches more nearly the type of the Polypodiaceae. 
The Foot . — The foot is formed mainly from the upper 
hypobasal quadrant, but encroaches more or less upon all the 
others. Very early its cells cease to show any definite order 
of division, and as they divide more slowly than those of the 
other organs of the embryo, while at the same time the whole 
foot enlarges, they soon become noticeably larger than the 
actively dividing cells of the other organs. The exact limits 
of the foot cannot be defined, as it merges insensibly into the 
other parts of the embryo, and in the later stages before the 
embryo breaks through the calyptra, occupies nearly or quite 
half of the entire embryo. This increase in size is due almost 
exclusively to simple expansion of the cells which become very 
large and nearly colourless. They lose most of their proto- 
plasmic contents, and serve simply as absorbent organs. They 
are in close contact with the cells of the prothallium, and 
encroach upon them until the foot penetrates deep into the 
prothallium (Figs. 95, 96), partially destroying the cells. The 
