i 36 Johnson. — On the Development of the 
laterally to several times their former size, and in so doing 
push the microsporangial cells around (Figs. 36, 37) to a 
position nearly at right angles to their former one. The 
macrosporangium mother-cell finally divides by three inclined 
walls to form the tetrahedral apical cell of the macro- 
sporangium (ma. sp., Figs. 32, 37). This apical cell cuts off 
two more segments on each of the three sides below (Fig. 41), 
which form the stalk and basal wall of the sporangium ; then 
a pericline is formed near the outer end of the apical cell, 
cutting off the archesporium (arc., Fig. 41) and completing 
the sporangium wall. The archesporium, as Russow has 
shown, then gives rise to the tapetum and spores. 
While the microsporangial cells are being pushed aside as 
described above, each has divided by anticlines approximately 
parallel to the segment wall, first to two (Fig. 36) and then to 
four (Fig. 41). These come to lie parallel to the segments of the 
apical cell of the macrosporangium, and are evidently the cells 
which Russow supposed to be segments of this, but there can be 
no doubt that they are really derived as described above. 
Of the four cells formed from each of the microsporangial 
cells as just described, the lower three go to form sterile 
tissue of the placenta (pa., Fig. 41), while only the upper one, 
next to the macrosporangium, actually forms microsporangia. 
Each of these upper cells divides by walls transverse to the 
axis of the sorus to form four cells on each side of each 
macrosporangium (which are well seen in a sagittal section 
of a capsule somewhat older than that shown in Fig. 43). 
Then each of these four cells swells out from the placenta, 
and divides into a basal cell (st. c., Fig. 41) and an outer cell, 
in which is formed later the tetrahedral apical cell giving rise 
to the stalk, walls, and archesporium. This basal cell of the 
microsporangium may be considered as homologous with the 
stalk-cell found in other Leptosporangiates, but nothing was 
seen in the development of the macrosporangium that could 
be regarded as such. In this latter respect Marsilia appears 
to differ from Pilularia, where Campbell (* 93 j states that such 
a cell is formed, at least occasionally. 
