364 Digby—The Cytology of Primula kewensis 
present in the heterotype prophase, owing to the undecipherable character 
of the nuclear phases that immediately precede and succeed it. During 
the rest which intervenes between the telophase of the last archesporial 
division and the prophase of the heterotype, the chromosomes resolve them- 
selves so completely that all trace of their identity is lost to view, and the 
arrangement of their units passes beyond the limit of interpretation. Again, 
during synapsis, the course of events is completely veiled by the dense 
tangle of the spireme. The parallel threads may either represent the 
pairing of whole univalent lengths of chromosome, according to Gregoire’s 
view (22), and in that case each thread would be homologous with a length 
of univalent beaded spireme of the premeiotic prophases, or they may 
represent the coming together of the halves of univalent lengths of 
chromosomes preparatory to the condensation for the whole somatic 
(univalent) chromosome. In Galtonia the homology between the parallel 
threads of the last premeiotic division (the result of the alveolization of 
each chromosome) and the parallel threads of the heterotype prophase 
can be traced through a continuous and progressive series. In both nuclear 
phases the parallel threads represent the longitudinal halves of the univalent 
chromosomes. During the telophase the process of the breaking up of the 
chromosomes and the distribution of their substance throughout the nucleus 
entail a separation of the longitudinal halves, whilst during the prophase 
the gradual evolution of the chromosomes involves an approach and an 
increasingly closer association of the longitudinal halves. It is believed 
that the same interpretation of the parallelisms found in the heterotype pro- 
phases may hold good for Primula , but for the reasons already given the 
surmise cannot be directly verified. Moreover, in Primula , as in other 
forms, it seems probable that the considerable thickening of strands may 
be due to the premature pairing of whole univalent chromosomes, a pairing 
which, in P. Jloribunda , is most clearly shown in the post-synaptic stages. 
When it is remembered that the completion of a mature bivalent chromosome 
entails not only the condensation of the two split halves of each univalent 
chromosome, but also the union of the two univalent chromosomes to form 
one bivalent combination, it does not seem irrational to believe that prepara- 
tions for both may be proceeding simultaneously in the presynaptic stages. 
The chromatic contents of the nucleus increase and concentrate into 
groups (Fig. 13), and diffuse throughout the linin. Gradually the whole 
masses together at one side of the nucleus. Parallelisms in the escaping 
portions can often be seen ; and faint strands of linin may extend to the 
periphery of the nucleus as loops, or apparently as free ends. At complete 
synapsis the chromatin mass has a very granular appearance, and is con- 
tracted into an extremely small space (Fig. 14). Primula does not conform 
to Lawson’s view (30) that there is no chromatin contraction during synapsis. 
The nucleolus is generally to be seen projecting from the synaptic knot, and 
