374 Digby. — The Cytology of Primula kewensis 
As the spireme comes out of synapsis the nucleolus continues to bud, 
with the result that many large rounded chromatin masses are caught 
up in the loops of the spireme (Fig. 73). In course of time these seem to 
become absorbed (Fig. 74), for they disappear, leaving only a few isolated 
beads, which are generally situated at the points of intersection of the loops 
(Fig. 74). The somewhat beaded character of the spireme recalls that of 
the sterile P. kewensis (Fig. 75). The beads are joined together by fine 
threads, and these tend to run in pairs, and where they meet there is always 
a chromatic swelling (Fig. 75). Even at this early stage in the pairing of 
homologous univalent spireme lengths it is possible to distinguish the 
skeleton of the future bivalent chromosomes. Gradually the paired portions 
of univalent spireme severally dissociate themselves from the others. At 
first these parallel threads have paired chromatin masses arranged at 
intervals along their length (Fig. 75), but as concentration proceeds less 
and less of the thread is visible, the chromatin becoming more diffuse 
(Fig. 76) ; as the sides of the chromosomes concentrate they become beaded 
(Figs. 77 and 78). 
When it is possible to identify the limits of the individual bivalent 
chromosomes, it is apparent that two are joined together end to end (Figs. 
79 and 80), forming as a rule a large looped figure. The univalent sides 
of each bivalent chromosome thicken, and often one or two chromosomes 
remain attached to the nucleolus (Fig. 81). Gradually the chromosomes 
become typically heterotype in shape (Fig. 83), and the large quadrivalent 
chromosome is most striking (Fig. 83). Then the heterotype chromosomes 
separate from one another, they become increasingly beaded (Fig. 84), and 
the fine threads joining them are tightly stretched. They stain less deeply 
and contract considerably (Figs. 85 and 86); the large chromosome often 
takes the shape of a ring (Fig. 86). After passing through this extremely 
beaded phase the chromosomes gradually lose their granular appearance 
and become slightly more condensed (Fig. 87), more homogeneous, and 
rounded in tmtline (Fig. 88). There is still further contraction of the 
chromosomes, each univalent chromosome of the bivalent combination 
becoming oval or rounded in shape (Fig. 89), the large chromosome appear- 
ing as a tetrad (Figs. 89, 90, and 91). The tetrad may be in the form of 
a square, or of a closed or partially opened ring, but in every case its fourfold 
character is evident (Fig. 91). The bivalent chromosomes are placed widely 
apart, and they are still connected to one another by fine threads. The 
nucleolus has by this time fragmented, and rounded globules of faintly 
staining nucleolar material may be seen adhering to the chromosomes 
(Fig. 92). Such is the peculiar and characteristic diakinesis of P. kewensis 
(fertile), the preparation for which is so prolonged. 
Several counts have been made of the chromosomes at this stage. 
Very rarely 18 bivalent chromosomes all of the same size are to be found ; 
