ANGIOSPERMS. 
forms the layer of fibrous cells which cause the dehiscence of the anther (Fig. 382, 
Gß)', to this we shall have to refer hereafter. 
The mother-cells of the pollen are at first large and their walls thin (Fig. 374, 
Ä, sm); but these increase considerably in thickness, though generally not uniformly 
(Figs. 375, 378, A), the thickening matter being usually distinctly stratified. In 
many Monocotyledons the mother-cells now become completely separated, the 
pollen-sac becomes broader, and the cells float singly or in connected groups in 
a granular fluid which fills up its cavity, as is shown in Fig. 374, B, a phenomenon 
Fig. 374. — Fimkia corclata ; A transverse section through a 
young pollen-sac before the isolation of the mother-cells sm, 
ep the tapetum which clothes the anther-lobe, 7u wall of the 
pollen-sac ; B the anther-lobe after isolation of the mother-cells 
sm; the tapetum (x 500). 
Fig. 375. — Mode of formation of the pollen of Funkia. 
ovata (X 550). In VII the wall of the daughter-cell has 
absorbed water till it has burst ; its protoplasm is forcing 
itself out through the fissure, and is lying before it 
rounded off into a spherical form. 
which calls strongly to mind the formation of the spores of Vascular Cryptogams. 
In other cases, however, as for instance in many Dicotyledons {TropcBolum^ Allhcsay 
&:c.), the very thick-walled mother-cells do not become isolated; they completely 
fill up the pollen-sac, but may become separated after the rupture of the anther- 
wall in water. In most Monocotyledons the large central nucleus divides, and 
two fresh nuclei make their appearance ; this is followed by the division of the 
protoplasm, and by the simultaneous formation of a cell-wall in the plane of 
division. The same process is repeated in each of the two cells, and thus the 
