378 Dig by . — The Cytology of Primula kewensis 
O. lata is crossed with 0 . gigas the F. I. generation shows 50 per cent, of 
a type intermediate between 0 . lata and 0 . gigas , and 50 per cent, 
intermediate between O. lamarckiana and 0 gigas. Lutz ( 32 ) experimented 
on crossing 0 . lata with 0 . gigas, and from a study of forty hybrid plants 
was able to divide them into three classes, both in respect to their external 
characters and to their number of chromosomes: (1) lata type with 15 
(2 x) chromosomes ; (2) gigas type with 30 (2 x) chromosomes ; and (3) 
intermediate type with 22 or 23 (2 x) chromosomes. 
General Comparisons. 
It is proposed to limit this brief discussion to the manner of union of 
the lengths of spireme in the formation of the bivalent chromosome; to 
the cytological detail of the nuclei of hybrids, especially with regard to 
the number of their chromosomes ; and to the fertile or sterile character of 
those hybrids. 
Firstly, as regards the origin of the bivalent chromosome. A mass 
of controversial literature has accumulated round certain disputed points, 
especially concerning the significance of the parallel threads in the presynaptic 
stages and whether the union of the univalent spiremes in the formation of the 
bivalent chromosome may be described as telosynaptic (11) or parasynaptic 
(22), and consequently whether the fission in the spireme separates two 
whole univalent chromosomes or whether it is the premature fission in the 
substance of the univalent chromosome which will take effect in the homo- 
type division. 
This series of Primula does not throw any light on the meaning of the 
parallelisms in the heterotype prophases. During the long rest between 
the last premeiotic and first meiotic divisions all sequence of events is lost, 
so that it is impossible to trace any relationship between the parallel threads 
of the heterotype prophases and the chromosomes of the preceding mitosis. 
Neither can any relationship be established between the parallel threads of 
the heterotype prophases and the parallel lengths of post-synaptic spireme, 
for during synapsis all proceedings are hopelessly obscured. Therefore 
whether each thread represents the longitudinal half of a portion of a uni- 
valent chromosome, and the pairing is the preparation for the condensation 
to form the whole univalent chromosome, or whether, according to the view 
held by Gregoire (22), each thread represents a portion of a whole univalent 
chromosome, and the parallelism is the premature pairing of homologous 
chromosomes, is a problem which cannot be solved by the study of Primula 
alone. Perhaps both arrangements may be proceeding simultaneously 
in the presynaptic prophases. Moreover, the interpretation of the parallel- 
isms does not materially affect the question as to the ultimate telosynaptic 
or parasynaptic origin of the bivalent chromosome, for it is the post- 
synaptic stages that elucidate this point. 
