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 qtiadrant walls, ultimately gives rise to the stem-initial, 

 lying close to the octant wall, /. c., 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 (</. ?'.). 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 hyphae, 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, merg-es 

 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 



