Sexual Nuclei in Lilium Mart agon. 471 
the spirem ribbon is still so narrow that in such small nuclei 
as we are now considering the double row of dots cannot be 
distinguished from a single row. I am the more inclined to 
believe it, as the double row of dots is found in the spirem 
stage of the second and third embryo-sac divisions, which in 
all other respects conform to the vegetative type (ante, p. 464). 
Supposing that this is the case, the difference between the 
vegetative spirem and that of the first embryo-sac nucleus 
would amount to this, that the change from a dotted to 
a homogeneous ribbon occurs early in the history of the 
vegetative spirem, while in the primary embryo-sac nucleus 
it is postponed until after segmentation has taken place. 
4. Segmentation of the spirem ribbon, that is its division 
into lengths by transverse fission, occurs in every karyo- 
kinesis. In that of the primary embryo-sac nucleus it is 
preceded by longitudinal fission of the whole spirem ribbon, 
whereas in the vegetative nucleus no traces of longitudinal 
fission can be perceived until the chromosomes are in position 
on the spindle. 
On the whole, we may conclude that the real departures 
from the vegetative type of karyokinesis shown by the 
primary embryo-sac nucleus occur during the earlier stages 
of development. They can only be partially referred to our 
ignorance of those stages in the history of the vegetative 
nucleus. Such distinctive features occurring at so critical 
a period as that immediately preceding the appearance of the 
reduced number of chromosomes cannot be without meaning. 
They certainly do not usher in a transverse division of chro- 
mosomes. It is difficult to believe that so long a preparation 
is needed in order to accomplish the mere reduction in 
number. For during the second karyokinesis in the embryo- 
sac, which follows on the first almost without interval, the 
chalazal nucleus exhibits from twenty-four to thirty-two chro- 
mosomes in its nuclear plate, though formed itself from 
the twelve chromosomes of the first division. The true 
explanation is still to be found. 
The question of the identity of the chromosomes throughout 
