THE YOUNG SPOROPHYTE. 39 
The two posterior upper octants (5, 6) divide irregularly into a mass of 
polyhedral cells, the foot. Those in contact with the base of the arche- 
gonium become closely applied to the wall, and the boundary between 
prothallial and embryonic tissues is often difficult to determine. Neigh- 
boring cells of the two anterior upper octants are also involved in the for- 
mation of the fully matured foot (figs. 235, 236, 246). 
Octants 2 and 7 divide irregularly and serve only to fill up their respec- 
tive corners of the embryo plant. Octant 1, after cleavages mostly parallel 
to the basal and quadrant walls, ultimately gives rise to the stem-initial, 
lying close to the octant wall, 7. e., near the median line. 
The lower anterior octants (3 and 4) elongate together in a horizontal 
direction (fig. 255). They unite at their anterior ends to form a group of 
marginal initials for the first leaf (cotyledon). This leaf, therefore, never 
possesses a single apical cell. 
As the leaf grows out, the whole anterior (epibasal) half of the embryo 
elongates, carrying forward both stem-initial and leaf. The plantlet lies 
horizontally. It consists of a short cylinder with root-initial at one end, 
leaf-initials at the other end, a dorsal papilla near the middle, in which is 
the stem-initial, and back of this a large dorsal protuberance, the foot, 
buried in the prothallus (fig. 246). The whole is surrounded by the greatly 
enlarged archegonial wall, the calyptra. The latter has become two or 
three cells thick all round (figs. 246, 255). Soon the leaf bursts through 
the calyptra and bends upward through the notch of the prothallus, and 
the primary root extends downward. The new plant is now independent, 
but the prothallus does not disappear until two or three leaves are formed 
(fig. 267). 
The young stem grows almost horizontally for 1 or 2 mm., increasing 
in diameter and complexity of structure until about five leaves have been 
formed. The stem then forks. The plant now differs only in size and 
sterility from the adult. The primary root grows about 5 cm. long, is 
slender, and has the structure of an adult rootlet (g. v.). It is not 
branched, but has copious root-hairs. Adventitious. roots arise in rapid 
succession, being sometimes as many, sometimes twice as many, as the 
leaves (fig. 256). They are like adult roots, only smaller. I have one 
specimen whose root-cells are densely filled with fungous hyphe, after the 
manner of the adult mycorhiza. The prothallus is also infected, but there 
is no connection (internally at least) between the fungous masses in sporo- 
phyte and gametophyte. 
The sporeling stem is short and cylindrical (figure 269). It is clothed 
with an irregular epidermis. The cortex, parenchymatous below, merges 
gradually into that of the adult region. The stele of the primary root is 
continuous with that of the stem. There is no line of demarcation on the 
ventral side, but dorsally a prominent angle of vascular tissue projects 
toward the foot (figs. 246, 247). Between this point and the insertion of 
