Sexual Nuclei in Lilium Martagon . 465 
chalazal one. I have not been able to trace any difference 
beyond that of size between the two nuclei during seg- 
mentation. The chromosomes when fully formed are quite 
as large in the chalazal as in the micropylar nucleus. Their 
number can be determined most easily somewhat later 
when the nuclear plate is formed. Exact results however 
are rarely to be obtained on account of difficulties of the 
same kind as those experienced in the previous division. 
They are increased in this case by the small size of the 
spindles and slender shape of the chromosomes. I have 
found but two micropylar spindles in which there could be 
no doubt about the number of chromosomes. In each case 
it was twelve. Twenty other micropylar nuclei allowed of 
approximate counting. In sixteen there were either eleven or 
twelve chromosomes, and in two either twelve or thirteen 
chromosomes. Of the two remaining nuclei one possessed 
either eleven, twelve, or thirteen, and one either ten, eleven, 
or twelve chromosomes. The exact number of the chromo- 
somes in the chalazal nucleus is of less importance, and the 
results much more uncertain on account of the crowded 
nuclear plate. Among twenty-five spindles in which the 
chromosomes could be approximately counted, one had about 
twenty, nine about twenty-four, five about twenty-eight, and 
ten about thirty-two chromosomes. 
Our object being to trace the formation of the ovum, we 
are strictly concerned with the micropylar nucleus only, and 
Figs. 29-31 are drawn from it. The chalazal nucleus how- 
ever goes through the same changes at the same time ; indeed, 
the correspondence between the two nuclei is very striking. 
They are always in exactly the same stage of division. 
The chromosomes gradually move into an equatorial plane 
to form the nuclear plate, but before this is accomplished the 
longitudinal fission of each can sometimes be observed. The 
separation of the segments takes place exactly as in the 
vegetative nucleus (cf. Figs. 30 and 31 with Figs. 6 and 7). 
Occasionally however a chromosome begins to open about 
the middle of its length (x, Fig. 30), just as those of the 
