Yasui. — On the Life-history of Salvinia natans . 471 
wall of the mature sporangium. The basal cell divides but few times, 
and forms the part of the wall attached to the stalk. 
The archesporial cell divides by the periclinal walls, forming three 
primary tapetal cells and a central cell (Figs. 8, 9). The central cell 
now divides by a wall more or less parallel to the long axis of the 
sporangium. It is soon followed by the next division, which divides two 
cells simultaneously by walls perpendicular to the first (Figs. 10-12). The 
quadrant-cells, thus formed, are again divided into equal octants (Figs. 12, 13). 
Each of these eight cells divides once more, and the sixteen microspore- 
mother-cells are formed (Fig. 14). During the divisions of the central cell 
the tapetal cells also divide by radial walls, but never by periclinal walls, so 
there is always one layer of tapetal cells, not two as described by J uranyi 
( 73 ). Juranyi adds, however, that the tapetal cells in the microsporangium 
are sometimes one-layered (Figs. 10-15). 
The full-grown microspore-mother-cell has denser cytoplasmic con- 
tents and a much larger nucleus than the surrounding cells of the sporan- 
gium. Its nucleus contains a large nucleolus and a delicate linin-reticulum 
in which small chromatin-granules are embedded (Figs. 14, 18). The nucleus 
soon prepares for division and shows the characteristic synaptic contraction 
(Figs. 15, 17). The synapsis stage lasts comparatively long, and it is fol- 
lowed by the spireme which comes out from the contracted nuclear contents 
(Fig. 18). The spireme then becomes shorter and thicker, and at last it 
segments into chromosomes. After the chromosomes are formed, kino- 
plasmic fibres appear in the cytoplasm surrounding the nucleus. Then 
the nuclear membrane begins to disappear and the multipolar spindle 
enters the nuclear cavity and comes in contact with the chromosomes. 
The spindle, when it is completely formed, assumes a bipolar structure 
(Figs. 19-22). 
The number of chromosomes is easily counted, as they are arranged at 
the equator of the spindle j the number is sixteen, and they are grouped in 
eight pairs (Fig. 21). Each half of the bivalent chromosomes now separates 
from the other and travels towards different poles of the spindle (Figs. 23, 
24). When the daughter-chromosomes reach the pole they remain for 
a short time unchanged, and this stage is also favourable for counting their 
number (Figs. 24, 25). 
As the spindle with a faint indication of a cell-plate at the equator dis- 
appears, two daughter-nuclei prepare for the second division. At the 
prophase of the division eight pairs of the chromosomes are distinctly 
visible (Fig. 27). The spindle is at first multipolar and later becomes 
bipolar. When the spindle is completely formed, eight bivalent chromo- 
somes arrange themselves at the equator. The sister-chromosomes of the 
same pair then separate one from the other and travel towards the pole 
(Fig. 28). Each of the four granddaughter-nuclei thus formed receives 
1 i 2 
