179 
A zo ! la filiculoides , Lam. 
well designated apical cells. The other cell in each octant 
divides by tangential and radial walls arranged with a good 
deal of regularity. By the growth of the two initial cells 
( x , x ') the young cotyledon rapidly grows at the lateral 
margins, and it bends forward so as to partly include the 
stem-apex. At the same time the upper marginal cells divide 
rapidly by oblique walls alternately on the inner and outer 
side, so that the cotyledon also grows in height. By this 
time the cotyledon has become about four cells thick. 
The Stem-Quadrant. 
As we have seen, the divisions in the stem-quadrant are not 
perfectly uniform. In case a two-sided apical cell is estab- 
lished at once, it divides from this time very much as in the 
mature plant. Each segment divides into a ventral and 
dorsal half, and each of these again into an acroscopic and 
basiscopic cell. In case the first division in the stem-quadrant 
divides it equally, it is not possible to say which of the cells 
will become the apical cell of the stem, but this is determined 
by the first division in each cell. One of the cells divides by 
a vertical wall into equal parts, and becomes the second leaf ; 
the other, as already indicated, forms regular segments. 
When the octant-cells are unequal, the smaller of the two, 
which may be considered as the first segment of the apical 
cell of the stem, becomes the mother-cell of the second leaf. 
At the base of the first leaf, between it and the stem, a group 
of short hairs (Fig. 71 h) is formed at an early stage. 
The Root. 
The primary root in Azolla arises in exactly the same way 
as in the other Leptosporangiatae. After the first division of 
the root-quadrant, one of the resulting octants becomes at 
once the apical cell. The first segment is usually cut off 
parallel to the basal wall of the embryo, and the next strikes 
it and the octant-wall (Fig. 66 c) so that the apical cell lies at 
this stage close to the octant wall. In the other octant of the 
