360 
Digby . — The Cytology of Primula kewensis 
sources, and in every case the doubled number of chromosomes has been 
substantiated. 
A similar example of the sudden duplication in the number of chromo- 
somes has been found amongst the Oenothera mutants ( 31 , 17 , and 20). 
O. gigas, which is known to have originated from O. Lamar ckiana , has 
14 haploid chromosomes, whilst O. Lamarckiana has only 7 haploid 
chromosomes. 
Another unlooked-for result has been obtained from crossing P. flori - 
bttnda isabellina with P. kewensis (seedling form) ( 29 ). This cross resembles 
that of P. floribunda isabellina crossed with P. kewensis (type) in external 
characters as well as in the number of the chromosomes. Both hybrids have, 
the typical P. floribunda number, 18 diploid and 9 haploid. In the case of 
P . floribunda isabellina x P. kewensis (type) this result would be expected, 
but in the case of P . floribunda isabellina x P. kewensis (seedling), where one 
parent has twice as many chromosomes as the other, there must have been 
some reducing process at work whereby the sum of 9 x + 18 x = 18 
An analogous reduction in the number of chromosomes in the hybrid, one 
of whose parents possesses a higher number than the other, occurs in 
the classical instance of Drosera obovata (33 and 34 ) and in a hybrid 
Oenothera. 
According to Geerts ( 20 ), when 0 . lata with its 7 haploid chromosomes 
is crossed with O. gigas with its 14 haploid chromosomes, at the first 
meiotic division the 7 homologous chromosomes pair and the 7 super- 
fluous chromosomes disintegrate. It may be that some such explanation 
may account for the elimination of the chromosomes in the Primida cross. 
Table of Primula Crosses with their Chromosome Numbers. 
P. floribunda P. verticillata 
18 (2 x ) 9 (x) 18 (2 x) 9 (x) 
P. kewensis (type) 
18 (2 x) 
9 (*) 
P. kewensis (seedling) 
36 (2 x) 
18 (x) 
I, 
P. kewensis farinosa 
36 (2 x) 
18 (#) 
1910. 
Seed Parent. 
Pollen Parent. 
Result. 
Chromosomes. 
P. floribunda 
P. verticillata 
P. floribunda 
18 (2 x) 
9 (■*) 
P. floribunda isabellina 
P. kezvensis (type) 
P. floribunda isabellina 
18 (2 x) 
9 {*) 
P. floribunda isabellina 
P. kewensis (seedling) 
P. floribunda isabellina 
18 (2 x) 
9 00 
P. verticillata 
P. floribunda 
P. verticillata 
18 (2 x) 
9 00 
P. verticillata 
P. floribunda isabellina 
P. kewensis farinosa 
36 (2 x) 
? 18 (af) 1 
P. kewensis (type) 
P. Horibunda isabellina 
No seed. 
1 The ( x ) number of chromosomes has not been counted, the most advanced pollen mother- 
nuclei being only in synapsis. 
