458 
J. Osawa 
cides nearly with the somatic number, which was found in the wall-cells 
of the young ovule. So the first nuclear division of the pollen-mother- 
cell may be the homotypic division and not the reducing one, at least 
in certain cases. In this case, it seems that the first mitosis is not some- 
tiraes followed by the formation of the seeond spindle, bnt the cell-wall 
is formed between these two daughter-nuclei, thns prodncing only two 
pollen-grains instead of the tetrad (Fig. 55), though exceptionally, each 
of them may divide mitotically. 
In the seeond ease, the spindle is narrower and the chromosomes 
are much larger, but less numerous than in the previous case just des- 
cribed (Fig. 56). Here the movement of the chromosomes towards the 
poles of the spindle goes sometimes very unevenlv, because some of the* 
chromosomes seem to move much more slowly than otliers, so that the 
chromosomes are scattered pretty irregularly on the spindle fibres (Fig. 57). 
In the anaphase of the first division we may count nearly twenty chromo- 
somes in each pole of the spindle. Thus we may conclude that the first 
division may sometimes be the heterotypic and reducing one, as in the 
case of T. officinale (Juel, 1905). In this case the seeond division of the 
pollen-mother-cell is the homotypic division (Figs. 59, 60), though many 
irregularities may take place at this stage and different number of chromo- 
somes may offen be found in different daughter-nuclei. 
In the telophase of the seeond division the nuclear membranes and 
nucleoli are produced in each daughter-nucleus and then the chromo- 
somes enter into the anastomosing condition, thus forming a tetrad as 
usual. 
In the pollen-development of T. albidum , there occur many irre- 
gularities and abnormalities besides those mentioned above. In many 
cases, the so-called extra-nuclear nucleoli were found very commonly 
during the heterotypic mitosis or during the amitotic division of pollen- 
mother-cell (Figs. 61—63). 
The amitotic division of the pollen-mother-cell was observed very 
often. In the diakinesis or earlier, the nuclei of mother-cells show various 
irregulär forms, some being dumb-bell- or hour-glass-shaped, others being 
irregularly branched, and others being drawn apart into two or more 
nuclei, variable in size (Figs. 61 — 63). Both mitotic and amitotic divi- 
sions are found in the same flower in different loculi of the anther. 
More than four nuclei are often found in a single tetrad, and these 
supernumerous nuclei may be produced in various wavs. The comparative 
slowness of the movement of some daughter-chromosomes towards the 
poles in the first division is sometimes the cause of these extra-nuclei, 
