and Development of Marsilea. 421 
superficial cells, and then continues dividing, sometimes by 
transverse and sometimes by longitudinal walls. The inner cell, 
which is now the true apical root-cell, proceeds to separate lateral 
cells of division alternately in three directions, which likewise 
originate the very uniform tissue of the root by longitudinal 
and transverse septa. At first, however, this process takes place 
very slowly. 
The most rapid progress is made by the first leaf. Its primi- 
tive cell is first broken up, simultaneously with the two sub- 
jacent cells of the anterior half of the germ, into two equal 
lateral halves, in a plane standing perpendicular to the first 
three divisional walls. In both, the further division takes place 
by the production of divisional walls alternately from above and 
from the front, tending towards each other internally, separating 
discoid cells from the apical cell, which is rising forwards and 
upwards. In this way the leaf soon acquires a conical form, 
constantly becoming more acute, which finally passes, by the 
repeated extension and division of the cells of the second and 
third order, into the filamentous form, which the first leaf 
retains. 
The evolution of the bud takes place but slowly. Its primi- 
tive cell is divided by the above-mentioned perpendicular septum 
into two adjacent cells, which are apparently similar, but are of 
very unequal value. One of them becomes the second leaf: the 
other continues to be the apical cell of the incipient axis of the 
stem; and thus the symmetry of the anterior side of the germ 
is for the moment destroyed. 
In the apical cell, three septa approximating internally, and 
running nearly parallel to the three lateral walls, separate three 
more divisional cells—first an upper ‘one, then a lower one, 
and lastly an inner lateral one adjacent to the second leaf: they 
leave the apical cell diminished between them, and are developed 
from no independent parts. The axis of the apical cell, which 
is now of a three-sided pyramidal form, furnished with a strongly 
arched basal surface directed forward, now exactly indicates the 
direction of the further development of the stem-bud. A seventh 
septum, running similarly to the fourth, but more strongly 
curved downwards on the side opposite to the second leaf, and 
cutting off a larger daughter cell, gives origin to the third leaf, 
which consequently makes its appearance opposite to the second, 
and restores the symmetry of the bud. 
Next trimerous cycles of interstitial cells issue from the apical 
cell, corresponding to its three walls, until the fourth and fifth 
leaves are produced from it in the same direction and in the 
same manner as the second and third. No law could be dis- 
covered for the number of these interstitial cells, which rapidly 
