37 1 
and of other related Primula Hybrids. 
P. kewensis (type) resembles P. verticillata in the tendency of the 
bivalent chromosomes, after their evolution, to segregate into two groups, 
and also in the formation of chains. 
As the spireme comes out of synapsis, it is much looped, and these 
loops intersect one another ; at the junction there is the usual chromatic 
swelling (Fig. 54). By the time that the nucleus has returned to the 
centre of the cell, portions of chromatin of one nucleus may be protruded 
into the adjoining cell, at the same time retaining a connexion with the 
mother nucleus (Fig. 55). This phenomenon has not been seen in the 
other species of Primula examined, and recalls a similar condition figured 
by Gregory ( 23 ) in the Sterile Pea. These chromatic protrusions when 
found in Primula are not nearly so striking as the ‘ bodies 5 which are 
thrown off in Galtonia (8), and moreover suggest possible nuclear 
degeneration. 
After the univalent loops have arranged themselves throughout the 
nuclear cavity, the spireme is as a whole much more beaded in character 
than is that of either of the parents. The beaded lengths of spireme 
arrange themselves in squares and in parallel lines, and in some places 
they unite to form the bivalent combination (Fig. 56). A single nucleus 
may exhibit very varied contents, for the same nucleus may have por- 
tions of its spireme in the beaded condition, whilst other portions may 
be homogeneous and pair as in P. floribunda (Fig. 57). Where the 
rows of beads, or the lengths of strands come together, there is always 
a decided thickening. A ladder-like condensation of univalent spiremes 
is of very common occurrence (Fig. 58). Strands may coalesce in one 
or more places, and create an undecipherable mass which may be described 
as an attempt to form a second contraction (Fig. 58). 
In P. floribunda there is a stage when all, or nearly all, of the uni- 
valent segments are joined in their homologous pairs prior to the 
final splitting apart. On the other hand, in P. kewensis (sterile), some 
of the univalent lengths may be in the act of pairing, whilst others may 
already be splitting apart, and it is possible that in some cases a close 
union of the univalent members of each pair may never be achieved. 
Gates ( 15 ) has described the attraction for pairing between homologous 
chromosomes as being very weak in the mutant O. rubrinervis . 
All stages in the splitting apart of the joined univalent segments may 
be seen (Fig. 59). These then concentrate and thicken, until the forms of 
the future bivalent chromosomes are recognizable (Fig. 60). When the 
bivalent chromosomes are individualized they tend, as in P . verticillata , to 
mass together into two groups (Fig. 61). When they again distribute them- 
selves throughout the nucleus chains of rings are constantly to be seen 
(Fig. 62), and, as in P. verticillata , it is evident that several rings go to form 
one bivalent chromosome. 
