Sexual Nuclei in Lilium Mart agon. 459 
from alcohol material I have never found free ends of chro- 
matic ribbon except where the nucleus is touched by the 
knife 1 . Nor are any anastomoses visible. The ribbon seems 
to consist of a single coiled and twisted erythrophilous fila- 
ment, bordered on either margin by a row of cyanophilous 
dots. Microtome sections about 10 /x thick from Flemming 
material show structural details of the ribbon very clearly, 
and it is possible, by careful comparison with the much 
thicker hand sections, to make sure that we are dealing with 
a true spirem stage. 
We are now approaching the point in the development 
of the embryo-sac nucleus at which the reduced number of 
chromatic segments first appears. The history of their 
development from the single ribbon of the spirem stage is 
undoubtedly the most important passage in the whole 
investigation. In order to appreciate the evidence it is 
necessary to anticipate a little and examine the structure 
of the mature chromosome 2 . Fig. 20 represents several 
chromosomes lying loose in the nuclear cavity before the 
appearance of a spindle. Each is composed of two segments 
which are twisted round each other. In some cases it is 
clear that these segments are quite distinct ; in others they 
seem to be joined at one end. It is impossible however to 
be certain that this appearance is not due to the close 
approximation of two free ends. At an earlier stage (Fig. 19) 
the chromosomes are longer, and each segment is an erythro- 
philous ribbon bordered on either margin by a row of 
cyanophilous dots. The figure is drawn from a median 
section in which the chromosomes are clustered round the 
nucleolus in a very characteristic way (Fig. 19). The ribbon- 
1 The preparation from which Fig. 14 was drawn for instance is not quite 
perfect. Four free ends are seen in the lower left-hand region, but these all lie in 
the same plane at the upper surface of the nucleus, and are therefore obviously due 
to the removal of a tangential section from that surface. 
2 As a matter of convenience I shall speak of the twelve chromatic segments 
which take part in the first karyokinesis of the embryo-sac nucleus as chromosomes. 
In doing so I do not mean to express any opinion as to their relation to the twenty- 
four chromosomes of the previous division. 
