192 Sargant . — Formation of the Sexual Nuclei 
4. The second karyokinesis divides the nucleus of each 
daughter-cell into two, and is followed by a corresponding 
cell-division (Figs. 16-22). 
Measurements of the pollen-mother-cell nuclei in the 
earliest stage show that they are then about the same size 
as the embryo-sac nucleus when just formed. They remain, 
however, for a much shorter time in the resting-state, and 
during that period do not increase so much in size. The 
embryo-sac nucleus is in the resting-state for about a fortnight, 
and during that time its mean diameter is nearly doubled 
(I, p. 455, and Figs. 10, 11). The nuclei of the pollen-mother- 
cells, on the other hand, do not retain the structure of a resting- 
nucleus for more than a day or two, and their mean diameter 
increases during that time by less than half its length. Indeed, 
the pollen-mother-cell nucleus is throughout its development 
smaller than the embryo-sac nucleus at corresponding stages. 
No doubt this is connected with the small size of the pollen- 
mother-cell as compared with the embryo-sac. I have drawn 
the pollen-mother-cells of the figures numbered 1, 2, 3-15 on 
the same scale as Figs. 10-26 in Part I for purposes of com- 
parison. When this scale has proved too small to show the 
necessary detail, portions of nuclei at corresponding stages 
have been drawn under a higher magnification (Figs. 1 a, 
2 a, &c.). 
The structure of the resting pollen-mother-cell nucleus 
corresponds exactly to that of the resting embryo-sac nucleus, 
though the detail is not quite so clear. A network of threads 
which seem to anastomose is partly obscured by the cloudy 
substance staining like dilute chromatin, which I have called 
amorphous chromatin. Here and there, in very deeply stained 
preparations, it can be seen that the threads are dotted ( x in 
Fig. 1 a), but this is less clear than in the embryo-sac nucleus. 
There are usually several spherical nucleoli (Fig. 1). 
As the nucleus increases in size, the amorphous chromatin 
is seen to be less generally distributed over the nuclear 
section. It is aggregated round the threads of the chromatic 
network, and seems to have diminished in bulk. Some con- 
