H7 
Double Fertilisation in Angiosperins. 
the primary nucleus of the sac: “four prothallial cells are formed ; 
of these two in the mean position j the mother cells of the oosphere 
and upper polar nucleus and of the uppermost antipodal and lower 
polar nucleus respectively] are gametogonia, which by a mitotic 
division form four gametes, three functional, one arrested. The 
apical cell [of the original four] forms an archegonium reduced to 
a two-cellular neck [synergidae]; the basal cell, forms two cells 
constituting a barren archegonium or mere prothallial cells” [the 
two lower antipodals]. The definitive or endosperm-nucleus he 
regards as a zygote formed by fusion of two gametes: the two 
polar nuclei. 
Nawaschin in 1898 published the following epoch-making 
observations: that whenever a pollen-tube was seen in contact with 
the embryo-sac both male nuclei were observed in the latter, were 
seen to have an almost cylindric long-club-shaped appearance, and 
to exhibit a worm-like contortion; they lay free in the sac and so 
close together as to appear like a single body. One of these two 
nuclei travelled to the ovum, the other to the upper polar-nucleus, 
to which latter it became applied; both nuclei retained their worm¬ 
like character. During the time that the one male nucleus was 
becoming more and more closely applied to the ovum, the polar- 
nucleus, along with the second male nucleus with which it was in 
contact, travelled to the other polar-nucleus and became attached to 
the latter in the middle of the sac. All the nuclei remained 
separate and distinct until the prophases of their division. The second 
male nucleus, which by this time had lost its worm like shape, was 
smaller, richer in chromatin, and possessed a coarser chromatin 
net-work than the polar nuclei, the lower of which latter is con¬ 
siderably larger than the upper. The character of the separate 
nuclei and composition of the nuclear groups were observed in a 
great number of fertilised ovules, so that there can be no doubt of 
the phenomenon being a constant one. Fusion of the three nuclei 
took place only after the prophases of division were completed; the 
same being true with regard to the fusion of the other male nucleus 
with that of the ovum. The formation both of the embryo and the 
endosperm was normal; in Fritillaria tenella the embryo, after 
reaching one-third of its size, died away, and the endosperm became 
absorbed. The ripe seed of Lilium Martagon contained a normal 
embryo. Nawaschin believed that, from the peculiar shape of the 
two male nuclei in these plants, they possess an independent move¬ 
ment like that of worms, 
