454 
J. Osawa 
eight chromosomes in the polar view. Thcn the chromosomes separate 
and the daughter-chromosomes move towards the poles of the spindle 
(Fig. 21). 
In the telophase of the second mitosis each group of eight chromo- 
somes enters into the anastomosing condition and finally the four 
daughter-nuclei are produced as usual (Fig. 22); thus the second 
division must he the equal and homotypic one. 
Shortly afterwards the cell-walls are formed between these four 
nuclei, producing a normal tetrad, and each of cells thus produced deve- 
lops finally into a pollen-grain. 
b) The development of the embryo-sac. 
The embryo-sac of T. platicarpum is originally derived from a hypo- 
dermal archesporial cell, situated at the apex of the nucellus. It is at 
first discernible as a large cell at the apex of the nucellus, directly un- 
derneath its epidermis, and it is easily distinguished from the adjacent 
cells by its larger size and its reactions towards stains. This cell becomes 
directly the embryo-sac-mother-cell without division and no parietal 
cell is ever found. The nucleus of the embryo-sac-mother-cell has the 
same structure as that of the pollen-mother-cell in presynaptic stage, 
as before mentioned. 
In the synaptic stage the threads gradually contract at one place 
of the nucleus and even when the synaptic ball becomes very compact, 
the constituent threads are yet recognizable more or less distinctly, and 
upon these linin-threads many small chromatin-granules are observable 
(Fig. 23). After a somewhat long duration of this stage the threads again 
loosen their structure and begin to extend in the nuclear cavity; the 
threads are then thicker and more distinct than in the presynaptic stage. 
As in the pollen-mother-cells, the double nature of the threads can be 
often detected distinctly under the favorable condition, e. g., in a looser 
portion of the spirem or in a thin tangential section of the nucleus (Figs. 24, 
25). These paired threads then again eonjugate to each other, forming 
a single homogeneous thick spirem as in the pollen-mother-cell (Fig. 26). 
The thread thickens, shortens and reaches the so-called “dolichonema” 
stage, whicli seems to last only for a little while and then the spirem 
reappears as double threads (Fig. 27). Düring the growtli of the spirem 
the cross-segmentation of the paired threads into the definite number 
of chromosomes takes place as in the pollen-mother-cell. 
Fig. 23 shows the paired chromosomes in the early stage of Seg- 
mentation; here the chromosomes take the appearance of long bentrod- 
