28 Dixon . — Fertilization of 
Immediately before fertilization radial striae can be seen 
extending from the nucleus of the oosphere into its surrounding 
protoplasm. These striae very probably precede a re-arrange- 
ment of the centrosomes of the nucleus as Guignard 1 found to 
be the case with the primary nucleus of the embryo-sac of 
L ilium. As a consequence of this rearrangement, the cen- 
trosomes of the female nucleus, which at first would be 
situated beneath the nucleus, owing to the fact that the ventral 
canal-cell is cut off from it shortly before (PL V, P'ig. 19), 
would separate from one another and take up a position 
on the equator of the female nucleus. The male nucleus when 
it enters the oosphere is very difficult to identify ; but I have 
observed several times similar striae round a nucleus which 
is in all probability the male nucleus. These striae would 
also indicate an adjustment of the centrosomes in its case. 
Accordingly, when the sexual pronuclei and their centrosomes 
unite, the new centrosomes formed by the fusion of the male 
and female centrosomes would lie in a plane perpendicular to 
the longitudinal axis of the archegonium. And so we would 
expect to find the first division of the oospore in a horizontal 
plane, as is in fact observed. 
Only one of the two male nuclei unites with the female 
nucleus in fertilization, the other remains in the protoplasm 
of the oosphere and is hard to distinguish from the two asexual 
nuclei coming from the pollen-tube. Why two sexual cells 
are formed when one is sufficient for fertilization, is difficult to 
explain. In the Angiosperms, where a similar division into 
two similar sexual cells takes place, Prof. Strasburger 2 has 
succeeded in observing, in one case, an oosphere which was 
fertilized by the two nuclei, a fact which proves conclusively 
that both are truly sexual cells. Perhaps the division of the 
body-cell into two sexual cells came about when the branching 
of the pollen-tube, before described (Fig. 8), was the rule, and 
when two branches at least had some probability of reaching 
different oospheres. Belajeff has observed that the pollen- 
1 Nouv. Etudes sur la Fecondation, Ann. des Sc. Nat., Bot., 1891, p. 181. 
2 Bef. bei den Phan., p. 64. 
