266 Welsford . — The Genesis of the Male Nuclei in Li Hum. 
only these vacuoles which mark the limit of the generative cell (Fig. 6), but 
later on a membrane is differentiated (Fig. 7). The generative cell takes 
the shape of that part of the pollen-grain wall against which it lies, merely 
bulging out to cover the nucleus. This is more clearly seen in a rather 
later stage when the generative cell has moved away from the wall. Fig. 8 
is a median longitudinal section of the ripe pollen-grain showing the peculiar 
shape of the generative cell, whilst Fig. 9 is a transverse section showing 
the nucleus lying in the centre of what appears to be a circular cell. 
A deeply staining granule may always be found at either pole of 
the generative nucleus ; they persist till a late stage, probably only dis- 
appearing when the cytoplasm of the sperm-cells disintegrates in the 
embryo sac. They may represent centrosomes, but no traces of spindle 
fibres were found near them. Granules are also sometimes found lying in 
a row, midway between the wall of the generative cell and its nucleus. 
They are extruded from the nucleus (Figs. 6, 7) and were seen to persist in 
the cytoplasm of the young sperm-cells (PL XVII, Figs. 24, 27), where they 
sometimes form a band-like structure. This is, however, better seen after 
they have passed from the pollen tube into the embryo sac, and is figured 
in the previous paper. 1 Their formation, later appearance, and the fact that 
they are often, but not always, present, suggest that they may be the vestiges 
of a blepharoplast. 
In the ripe pollen-grain, before the anther has dehisced, the chromatin 
of the generative cell always stains more deeply than that of the tube 
nucleus; it is, indeed, already preparing to divide. Nuclear division, how- 
ever, was never found to occur before germination in Lilium auratum , the 
nucleus being invariably in the spireme stage when passing into the tube. 
Material fixed two hours after pollination showed various stages ; in some 
cases the pollen tube was only just growing out, whilst in others the young 
tube contained a generative nucleus in the anaphase condition. Fig. 10 
shows a young pollen-grain which has germinated and in which the two 
nuclei have not passed into the tube. The cytoplasm has a very streaky 
appearance, indicating that the nuclei are carried out passively by the 
streaming protoplasm. 
Unfortunately the pollen tubes of Lilium auratum at this stage are 
lying on the stigma and are so twisted that it was found almost impossible 
to study the stages of nuclear division with accuracy or to make satisfactory 
drawings of them. The generative cell of Lilium Martagon divides after 
the pollen tube has grown into the stylar canal, where it keeps a com- 
paratively straight course ; consequently a description of the division of the 
generative cell has been given of this plant instead of Lilium auratum. 
Sufficient preparations, however, were obtained of Lilium auratum to show 
that the stages of division are very similar in the two species. 
1 Loc. cit., Blackman and Welsford, Plate XII, Fig. 6. 
