586 TRANSACTIONS OF SECTION K. 



As regards the numbers of the chromosomes in the various generations, the 

 parents of P. kewcnsis (sterile) have identically the same number of chromosomes, 

 and, as might be expected, this number is repeated in the hybrid. Thus P. 

 fioribvnda, P. verticillata, and P. kewcnsis (sterile) all have 18 (2 x) and 9 (x) 

 chromosomes. The surprising phenomenon occurs in the seedling, P. kewensis, 

 for there, instead* of the familiar 18 (2 x) and 9 (x) chromosomes, there are 

 36 (2 x) and 18 (x) chromosomes. 



By some means either at, or subsequent to, the fertilisation of the ' pin flower ' 

 on the sterile stock the number of chromosomes has been duplicated. This doubled 

 number is continued throughout the generations of the fertile P. kewensis, and 

 is also characteristic of the variety, P. kewcnsis farinosa. 



This increase in the number of chromosomes cannot be accounted for by 

 apogamy. The divisions of the embryo sac mother nuclei of both the sterile 

 and of the fertile forms are normal, and in the one case 9 (x) chromosomes, 

 and in th© other 18 (x) chromosomes are to be seen at meiosis, while in the sur- 

 rounding tissue there are correspondingly 18 (2 x) and 36 (2 x) chromosomes. 



The doubled number of chromosomes has since reappeared in a cross made in 

 1910 by Coutts, the foreman, at Kew, between P. verticillata and /'. flori- 

 hunda var. isabellina. The resulting hybrids not only resemble P. kewensis 

 farinosa in their external features, but also possess 36 (2 x) chromosomes. 



This remarkable sudden duplication of chromosomes has its counterpart in 

 the Oenotheras. IE. Lamarckiana has 14 (2 x) and (7 x) chromosomes, while (E. 

 gigas, which mutated from IE. Lamarckiana, has 28 (2 x) and 14 (x) chromosomes. 

 Like the fertile P. kewensis, CE. gigas has again arisen from other sources — once 

 as a hybrid, and once from a pure strain of (E. gvblinervis. In the Oenotheras, 

 as there is no evidence of the addition of new unit characters, the doubling of 

 the chromosomes is believed to be brought about by longitudinal fission. In the 

 Primulas the phenomenon is apparently associated with the change from the 

 sterile to the fertile condition. 



One other interesting fact has emanated from the 1910 Primula hybrids. 

 P. floribunda var. isabellina, with its 18 (2 x) and 9 (x) chromosomes, when 

 crossed with P. kewensis, seedling form, wit'.i its 36 (2 x) and 18 (x) chromo- 

 somes, has offspring which resemble the seed parent, /'. fioribvnda var. isabel- 

 lina, both in external characters and in the number of the chromosomes. By some 

 regulating process the sum of 9 (x) + ]8 (x)=18 (2x). 



Again, an analogy is to be found in the Oenotheras. (E. lata, ]4 (x) and 

 7 (x) chromosomes, crossed with (E . gigas, 28 (2 x) and 14 (x) chromosomes, re- 

 sults in a hybrid with 21 (2 x) chromosomes. According to Geerts, at meiosis, the 

 seven homologous chromosomes, derived from cither parent, pair, the seven 

 supernumerary unpaired chromosomes disintegrate. In this way the x number 

 of chromosomes in the hybrid is reduced to that of the parent which possesses 

 the lowest number. 



Such are the facts concerning the chromosomes in the parents of the hybrid 

 P. kewensis, in the hybrid itself, and in the ensuing generations. A detailed 

 and comparative account of the cytology of this series of Primulas will be 

 published shortly. 



6. On the Flora of Shetland, with some reference to its Ecology 



By W. West. 



7. The Occurrence of Oidium Enonymi-Japonic.ie in Southern England. 

 By Sir Daniel Morris, K.C.M.G. 



8. Report on the Structure of Fossil Plants. — See Reports, p. 176. 



9. Report on the Experimental Study of Heredity. — See Reports, p. 176. 



