298 Sir as burger. — The Periodic Reduction of 
fact that the number of the chromosomes in the nuclei of 
the somatic cells of both the sexual and the asexual genera- 
tions has been found to vary. But, so far as my experience 
goes, these variations are always to be observed in the nuclei 
of cells which are not longer embryonic, like those in an 
embryo or in a growing-point, but which, on the contrary, 
are to some extent histologically specialized and are not 
destined to eventually give rise to reproductive cells. Both 
Guignard and I have often observed variation in the number 
of the chromosomes in the cells of the nucellus and integu- 
ments of the ovules. The determinate number of chromo- 
somes is still more frequently departed from in nuclei which 
are definitively excluded from the sphere of reproduction. 
Thus Guignard 1 found in species of Lilium that the lower 
nucleus in the embryo-sac, from which the antipodal cells 
are derived, has not twelve chromosomes like the upper 
nucleus which gives rise to the egg-apparatus, but sixteen, 
twenty, or even twenty-four chromosomes. The secondary 
nucleus of the embryo-sac, by the division of which the 
development of the endosperm is initiated in the Angio- 
sperms, is produced by the fusion of the two (upper and 
lower) polar nuclei, and must therefore contain as many 
chromosomes as both the polar nuclei. Hence, in Lilium , 
the nuclei of the endosperm are usually found to contain 
more than twenty-four chromosomes, although it represents 
the generation which typically possesses only twelve chromo- 
somes in each nucleus. Some time ago 2 I described the 
frequent nuclear fusions which gradually take place in the 
developing endosperm of the Angiosperms when, as the cell- 
areas are being marked out, each area encloses several nuclei. 
As regards the Gymnosperms, Dixon was able to ascertain 
that, in Pinus sylvestris , the determinate number of chromo- 
somes was adhered to in the prothallial nuclei of the embryo- 
sac, until the development of the archegonia : but when the 
development of the archegonia is initiated, the determinate 
1 Nouvelles Etudes, p. 187. 
2 See especially, Zellbildung und Zelltheilung, 3. Aufl., 1880, p. 25. 
