219 
Pollen Mother-cells of Li Hum canadense . 
nuclei of the first division in the pollen mother-cells of Angiosperms. In 
Podophyllum and Helleborus , however, according to Mottier (’97), nucleoles 
appear in these nuclei. 
The nucleus lies very close to the cell-wall ; its outline, when the 
nuclear membrane first appears (Fig. 91), is irregular, especially on the side 
toward the equatorial plane of the spindle ; as the nucleus grows it becomes 
more rounded (Fig. 92), but remains always flattened in the axial plane 
of the spindle. 
While the nucleus is growing, the chromosomes seem to stretch out, 
becoming longer and slenderer (Figs. 92, 93). Their free ends, extending 
toward the equatorial plane of the spindle, become curved in such a way as 
to bring the end of one arm of a V into contact with the end of an arm of 
another V ; these ends then apparently fuse. At the same time, the ends 
by which the granddaughter chromosomes were in contact at the angles 
of the V’s also seem to have fused, the final result being a single continuous 
closed spirem. Fig. 92 shows the spirem, viewed laterally, at the time of 
the formation of the cell-plate ; Fig. 93 shows an oblique view of the 
nucleus after the completion of cell-division. From these figures it appears 
that, although the strands of the spirem become somewhat bent and curved, 
they still retain the general form which results from the joining of the 
V-shaped chromosomes in the manner just described. Looking at the 
nucleus, therefore, as in Fig. 93, one sees a sort of rosette, formed by 
the arms of the V’s diverging from an open space about what was formerly 
the polar region, the spirem lying almost entirely in the peripheral region 
of the nucleus. The nucleus never passes into anything resembling a resting 
condition. A few achromatic fibres are sometimes seen attached to the 
spirem strands ; but the latter retain their distinct outlines and show no 
sign of breaking up or reticulation. I do not find, as did Mottier (’97) 
at the time of the formation of the cell-plate, a shortening of the spindle 
fibres and a closer approximation of the daughter nuclei ; in Lilium 
canadense the nuclei remain near the cell-wall in about the positions 
occupied by the poles of the first spindle. 
The Homoeotypic Division. 
The Prophases . 
While the processes involved in the division of the pollen mother-cell 
nucleus extend over a very long time, the succession of events in the 
division of the daughter nuclei is extremely rapid. Practically the whole 
series of stages may often be traced within a single anther sac. 
The first evidence of a preparation for the new division is seen in 
a further increase in size of the nucleus, accompanied by a loosening 
R 
