2o6 Sargant . — Formation of the Sexual Nuclei 
29 in Part I with Fig. 18 in this part). Another difference 
must also be mentioned. In the embryo-sac the young 
chromosomes when just formed from the spirem -ribbon are 
of different shapes, often hooked at one or both ends [I, Fig. 
29). Most of those formed from the daughter-nucleus of the 
pollen-mother-cell are alike and of a perfectly definite shape, 
which may be described as a V with the angle bent back 
(Fig. 18, Nos. 1, 2, 3, 4, 5, and 9). This is the characteristic 
form of the diaster-segments in the previous division (Fig. 14). 
A few are irregularly twisted (Fig. 18, Nos. 6 and 7), and 
others still show the median bend characteristic of the 
V-shape, though they are straightening out (Fig. 18, No. 8). 
This peculiarity of shape suggests that the daughter-chromo- 
somes of the first division have retained their identity within 
the daughter-nucleus. 
The chromosomes do their best to form an equatorial plate 
as soon as the spindle is formed. They are necessarily much 
crowded together. The whole pollen-mother-cell was barely 
large enough for the spindle of the first karyokinesis. The 
chromosomes which take part in the second are fully as long 
as the mother-chromosomes, though less thick. But the 
pyramidal mother-cell has been divided by a partition into 
two compartments of awkward shape. The spindle formed 
in each is usually more or less distorted to fit it (Figs. 20, 22). 
The long slender chromosomes have to fit as best they may 
into the equatorial zone of this spindle (Fig. 20). 
This crowding together of the chromosomes on the spindle 
makes observation of the details of karyokinesis somewhat 
difficult. At least two different accounts have been given 
of the "way in which actual separation of the chromosome- 
segments takes place 1 . I have found thick sections useless, 
because in a preparation which includes the whole of a nuclear 
plate one chromosome cannot be distinguished from another. 
Very thin sections are apt to be misleading, as they rarely 
1 (i-) Guignard, Nouvelles Etudes sur la Fecondation, p. 176 ; J. B. Farmer, 
Ueber Kerntheilnng in Lilium-Antheren, Flora, 1895, p. 67. (2) Strasburger, 
Botanisches Practicum, III. Aufl. p. 61 1. 
