32 
Dixon. — Fertilization of 
Summarizing, then, the numbers of the chromosomes in 
the gametophyte, we have : 
Nuclei of Prothallium (endosperm) . . 8. 
Nuclei of walls of archegonium . . 8,12,24. 
Nuclei of oosphere and ventral canal-cell . 8. 
From these numbers we see that Overton’s generalization 
is not applicable to Pinus silvesPis at least. For, just as 
Guignard observed that in the embryo-sac of L ilium Mart agon 
the lower nucleus resulting from the division of the primary 
nucleus of the embryo-sac has a greater number of chromo- 
somes than the upper one, so here there is in certain nuclei 
of the embryo-sac a larger number than in others. It is also 
remarkable that neither in Pinus nor in Lilium is this 
increased number constant; in the former 8, 12, 24 were 
counted, while in the latter Guignard observed 16, 20, 24, 
whereas the oosphere and its sister- nuclei had only J2 
chromosomes. It seems probable that in both cases the 
reduced number is only rigidly adhered to by all the nuclei 
of the gametophyte till a few cell-generations before the 
division which gives rise to the oosphere, and that at this 
point there arise two distinct cell-families, one with the 
reduced number to which the oosphere belongs, and the 
other with a larger variable number of chromosomes which, 
in the Lily, gives rise to the lower half of the secondary 
nucleus of the embryo-sac and the three antipodal cells, while 
in Pinus it gives rise to the cells forming the wall of the 
archegonium. In this way we may regard the synergidae, 
the upper ‘ polar nucleus ’ and the oosphere of Angiosperms 
as homologous with the endosperm and oosphere of Gymno- 
sperms, while the lower c polar nucleus ’ and antipodal cells of 
the former would correspond to the cells of the wall of the 
archegonium of the latter. 
In the male gametophyte, on the other hand, we could not 
expect to find an increase of the number of chromosomes, as 
neither of the asexual nuclei divides after the mother-cell of 
the two generative cells is formed. 
