546 



MOSSES AND FERNS 



CHAP. 



but in several young embryos examined, no definite octant walls 

 were present, at least in the upper octants, but whether this 

 is a common occurrence would be difficult to say. The next 

 divisions in the embryo resemble those in Marattia, and as in the 

 latter it may be said that the young members of the embryo 

 grow for a short time from an apical cell, inasmuch as the tetra- 

 hedral octants at first have segments cut off parallel with the 

 basal, quadrant, and octant walls, leaving an outer cell (Fig. 

 314, A) that still retains its original form; but very soon peri- 



FiG. 314. — A, An embryo of I. echinospora van Braunii, with unusually regular 

 divisions, X450; B, a much older one, still enclosed within the prothallium, X150; 

 ar, archegonia. 



clinal walls arise in this cell in each quadrant, and it is no longer 

 recognisable as an apical cell, and from this time the apex of the 

 young member grows from a group of initial cells. 



Up to this time the embryo has increased but little in size, 

 and retains the globular or oval form of the Qgg. It now 

 elongates in the direction of the basal wall, and soon after, the 

 cotyledon and primary root become differentiated. The axis 

 of the former coincides with the plane of the basal wall, and it 



