Allen—Spermatogenesis and Apogamy in Ferns . 28- 
but two or three times the size of one of the adjacent prothal- 
lial cells, consists of twenty-five or thirty cells. The well-de¬ 
fined surface layer of this compact mass is composed of small 
irregular cells. In the interior of this mass, repeated tangential 
divisions have resulted in several layers of still smaller tabular 
cells. ISTo apical cell can be distinguished at this stage. The 
limits of the sporophytic tissue are well defined. 
As this compact mass of embryonic tissue grows larger, the 
contrast in size between its cells and the adjacent prothallial 
cells becomes less marked. It is still possible to determine the 
limits of the sporophytic tissue, however, when the outgrowth 
is large enough to be seen with the hand lens. (Figures 39 and 
40.) 
The prothallium is now three cells thick for a short dis¬ 
tance back of the sporophyte. The tangentially placed walls 
in the mass are still conspicuous, bounding the flat cells which ex¬ 
tend in rows radially from the center of the mass to its outer 
surface. (Figure 39.) At a still later stage, as shown in fig¬ 
ure forty, the arrangement of the cells is somewhat more ir¬ 
regular. Cell differentiation has begun at this stage. There 
is a series of fully formed tracheids in the interior of the mass 
and the chromatophores of the outer layer of cells contain good 
sized starch grains. 
In its further growth, an apical cell is differentiated at the 
outer anterior angle of the young sporophyte. „ This by growth 
and division gives rise to the first leaf. In the hollow between 
the base of this leaf and the prothallium the apex of the stem 
is organized. The first root arises endogenously and pushes 
backward from a point near ihe base of the first leaf. Figure 
forty-one shows a somewhat oblique section of a sporophyte in 
which the root (r) is just breaking through the tissues. The 
young incurved leaf (1) protects the stem apex (s) which lies 
near its base. A strand of vascular tissues runs from the leaf 
tip back toward the root. The section is slightly oblique and 
the missing part of the vascular strand is found in adjacent 
sections. The leaf and stem of the young sporophyte are cov¬ 
ered with glandular hairs of the same form as those found! 
upon the prothallium. 
