146 Double Fertilisation in Angiosperms. 
comes to occupy a central position in the cell-cavity. At maturity 
of the cell this primary nucleus divides into two daughter-nuclei, 
each of which travels to one end of the sac. Then each divides by 
two successive divisions until four nuclei are formed at each end of 
the sac. One of these four from each end then travels to the 
centre of the sac, and, sometimes before, sometimes after, fertili¬ 
sation takes place, these two polar nuclei fuse together to form the 
definitive or secondary nucleus of the embryo sac. Meanwhile, each 
of the three nuclei at the micropylar end of the sac becomes 
invested with protoplasm enclosed by a delicate membrane; a pair 
of these cells, usually somewhat elongated, at the extreme end of 
the sac become the synergidae , while the third and larger cell 
becomes the oosphere or egg-cell. At the chalazal end of the sac 
three antipodal cells are formed, and these are often much more 
conspicuous than the cells at the micropylar end. 
Hofmeister 1 considered that all the nuclei of the sac possessed 
primitively the same value and any one of them could develope into 
an embryo. The sole function of the antipodals was that of 
elaborating substances for the embryo. 
Vesque 2 and Warming 3 both regarded the embryo sac as the 
product of fusion of two cells, and the four nuclei finally formed at 
each end of the sac were the representatives of the spores resulting 
from the divisions of these two spore-mother-cells. 
Guignard 4 held that all the cells in the sac were endosperm- 
cells; that the oosphere was a reduced archegonium; that the 
synergidae were endosperm-cells which had become adapted to a 
new function ; and that the antipodals are either an organic 
residuum of the sac or a reduced prothallus ; but he eventually 
regarded the prothallus as consisting of the sexual apparatus, 
antipodals and the two polar-nuclei. 
Hartog 5 believed that, as a result of two successive divisions of 
1 “ Neue Beitrage zur Keiiutniss der Rmbryobildung der 
Phanerogamen ”; (Abhandl. d. Konigl. Gesellsck. d. Wiss. ; 
Vol. v., p. 671). 
2 “ Developpeinent du sac embryoimaire des Plianerogames 
Angiospermes ”; Aim. d. .Sciences Nat. Hot., ser. 6, Vol. vi., 
1878. 
“ Nouvelles recliereliessur le developpeinent du sac embryon- 
naire ” ; Ditto, ser. 6., Vol. viii., 1879. 
3 “ Beinerkungen iiber das Richen ” ; Hot. Zeit. 1874. 
De 1 ’ Ovule ” ; Ann. d. Sci. Nat. Hot. ser. 6, Vol. v., 1878. 
Bull, de la Soc. Bot. de France, Vol. xxviii., 1881. 
Ann. d. Sci. Nat. Bot. ser. 6, Vol. xii., 1881. 
Ann. d. Sci. Nat Bot. ser. 6, Vol. xiii., 1882. 
5 “ Some Problems of Reproduction : a Comparative Study of 
Gametogeny and Protoplasmic Senescence and Rejuvenes¬ 
cence.” (Quart. Journal Microx. Science, Vol. xi., 1891). 
