Life-History of Isoetes . 
243 
The Embryo. 
The youngest embryos observed had the first division-wall 
already complete (Fig. 19). This is transverse, but more or 
less inclined to the axis of the archegonium. The nuclei of 
the two cells are large, and contain several chromatin-masses. 
The second divisions in the two halves of the embryo do not 
always occur simultaneously, the lower half dividing some- 
times before the upper, and at times the first walls in the two 
parts are at right-angles to each other instead of in the same 
plane, as is usual. Of the quadrants resulting from these 
divisions, the two lower form the foot, which is here large, 
and of the upper one forms the first leaf, and the other the 
primary root. The apex of the stem, which always is very 
inconspicuous, arises between the bases of the leaf and root, 
and probably belongs to the same quadrant as the latter ; but 
as it does not project at all, and is not certainly recognisable 
until after the boundary between the quadrants is no longer 
evident, this cannot be asserted positively. 
Sometimes (see Fig. 31) the quadrants divide by vertical 
walls into nearly equal octants, but in several young embryos 
observed (see Fig. 25) no regular octant-wall was formed, at 
least in the upper quadrants, but whether such irregularities 
were normal it is difficult to say, and it is certain that some- 
times, at any rate, and probably in most cases, the embryo is 
divided into regular octants as in the ferns. 
The next divisions also follow much the same plan as in the 
fern-embryo, and for a short time the young members may be 
said to grow 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. 24, a) 
that still retains the original form ; but very soon periclinal 
walls are formed in this cell in each quadrant, and it is no 
longer recognisable as an apical cell. Unfortunately, on ac- 
count of the great difficulty of making successful sections of 
the very young embryos, it was not possible to get a sufficient 
