284 MOSSES AND FERNS chap. 



always occur simultaneously, the lower half sometimes dividing 

 before the upper one, and at times the second walls are at 

 right angles instead of in the same plane. Of the quadrants 

 thus formed, the two lower form the foot, and the two upper 

 ones the cotyledon and primary root. The stem apex arises 

 secondarily at a later period, and probably belongs to the 

 same quadrant as the root ; but as it does not project at all, 

 and is not certainly recognisable until after the boundaries 

 between the quadrants are no longer evident, this cannot be 

 positively asserted. 



Sometimes the quadrants divide into nearly equal octants, 

 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 tetrahedral octants at first have segments cut off parallel 

 with the basal, quadrant, and octant walls, leaving an outer 

 cell (Fig. 149, A) that still retains its original form ; but very 

 soon periclinal 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 &^^. 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 

 approaches more or less the vertical as the latter is more or 

 less inclined. Occasionally the basal wall is so nearly vertical 

 that the cotyledon grows upright and penetrates the neck of 

 the archegonium at right angles to its ordinary position. At 

 the base of the leaf at this stage a single cell, larger than its 

 neighbours, may often be seen (Fig. 150, /). This is the 

 mother cell of the ligule, found in all the leaves. This cell 

 projects, and as the leaf grows divides regularly by walls in a 

 manner compared by Hofmeister to the divisions in the 

 gemmae of Marchantia. It finally forms a scale-like appendage 

 about twelve cells in length by as many in breadth. 



Almost coincident with the first appearance of the ligule 



