Welsford . — The Genesis of the Male Nuclei in Lilium. 267 
Soon after the generative cell of Lilium Martagon has passed into the 
tube its nucleus enlarges, often almost hiding the cytoplasm ; in PL XVI, 
Fig. 11 it is seen to be much spread out and to be lying over one of the polar 
granules. The outline of the generative cell is still clearly visible at the stage 
shown in Fig. 12 before the split thread has divided to form the chromo- 
somes. From this time the generative cell increases greatly in size and 
becomes less clearly marked, though it is differentiated from the more 
vacuolate protoplasm surrounding it. After the cytoplasm has spread out 
and before the chromosomes pass into the metaphase the chromatin 
material is often found to lie in a curved mass suggesting a wriggling 
movement (Figs. 13, 14) ; later, however, owing to the narrow space of the 
tube, it spreads out and the twelve longitudinally split chromosomes are formed 
(Figs. 15, 1 6, 17). No spindle fibres were seen at any stage of the division, 
the twenty-four long thin daughter-chromosomes being massed together as 
is shown in PL XVII, Fig. 19. The chromosomes now separate, and as the 
two groups move apart each is seen to be surrounded by a separate mass of 
cytoplasm (Fig. 20). The nuclei of the two male cells pass into the spireme 
condition and soon assume the curved or humped sausage shape with 
pointed ends so characteristic of the mature sperm. Nuclei at this stage 
were found at about 2 mm. from the apex of the stigma and presumably had 
at least a further 10 mm. to travel before reaching the micropyle ; this they 
usually do whilst still surrounded by their cells (Figs. 2 6, 27), but sometimes 
the cells are left behind (Figs. 24, 25), or are attached to one end of the 
nucleus (Figs. 21, 24, 29). Fig. 27 shows two male cells of Lilium auratum 
about 3 mm. from the apex of the stigma. 
Figs. 28, 30, 31 are drawn from pollen tubes dissected from the base 
of the style of Lilium auratum six days after pollination and about three 
days before fertilization will take place. The male cells are clearly seen, 
their nuclei being either curved or straight ; the lobed tube nucleus lies 
a little way in front of the male cells. At this stage the tip of the pollen 
tube is generally somewhat enlarged and often thickened (Figs. 27, 28). 
The function of this enlargement was not ascertained ; perhaps it may be of 
use in pushing apart the cells of the micropyle. In Fig. 32 two male cells 
are seen in the micropyle of Lilium auratum , but in Fig. 33 the nuclei have 
escaped from their cells and are lying free in the cytoplasm of the pollen 
tube. The pollen tube actually enters the embryo sac and preserves its 
shape, at any rate till after fertilization is accomplished, becoming filled with 
densely staining disintegrating matter after the escape of the two sperm 
nuclei. This was clearly shown in one preparation where a slight pressure 
on the cover-slip caused the tube to move slightly and brought its wall into 
prominence against the vacuolate cytoplasm of the embryo sac. The two 
male nuclei were invariably found to escape from their cells before leaving 
the pollen tube to pass across the embryo sac. 
