tiecent Papefs on CEnothera Mutations. ig^. 



and rubrinervis, treating them both anatomically and chemically. 

 He points out that the differences between Lamarckiana and 

 rubrinervis, are analogous to those between the twin types IcBta and 

 velntina produced in such a cross as biennis x Lamarckiana ; and 

 he believes that Lamarckiafta and rubrinervis are each under 

 certain circumstances capable of giving rise to the other. This 

 view is borne out by certain results of the reviewer. It is also 

 of interest that several collections of wild seeds of O. innricata from 

 widely sundered parts of Canada show a corresponding dimorphism 

 (21), indicating that such a condition may be widespread in this 

 section of the genus. 



Three cytological papers have been published by Davis (4, 5, 6) 

 which are in large part a confirmation of the earlier results of Gates 

 (13a, etc.) It was found, however, that in O. grandiflora the pairing of 

 the chromosomes in synapsis was closer than in either biennis or 

 Lamarckiana, closed rings being formed by the chromosome pairs 

 in diakinesis, while in the latter two species and their derivatives 

 the homologous chromosomes are very loosely paired or not paired 

 at all at that time. Hence it appears that the attraction which 

 causes pairing is greater in O. grandiflora than in the other species. 

 As I have pointed out, the loosely paired condition gives greater 

 opportunity for irregularities, such as actually occur, in the 

 distribution of chromosome pairs during meiosis. It is now certain 

 that this process is concerned in the appearance of some of the 

 mutations (lata and semilata). 



In a detailed account of somatic mitoses in CEnothera, Gates 

 (17) found the number of chromosomes in an individual to be 

 constant, the rare exceptions in metaphase groups being explicable 

 in entire accord with the belief in the genetic continuity of chromo- 

 somes from cell to cell. Certain peculiar cases were found in the 

 cells of the nucellus in 0. lata, in which the chromosomes were 

 closely paired in metaphase as though about to undergo a reduction- 

 division, though the chromosomes retained their somatic shape. 



Several recent papers have dealt with the question of the 

 origin 0. gigas. There have been two chief views on this subject. 

 Gates, in 1909, in showing the increased size of the cells and nuclei 

 in gigas as compared with Lamarckiana, indicated the probability 

 that the chromosome-doubling to give twenty-eight occurred in the 

 fertilized egg or the young embryo, through a suspended mitosis. 

 It was further pointed out that in various wild species the Ax 

 number of chromosomes had probably originated in the same way. 

 Strasburger (30) entirely concurred in these views and extended 

 them to cover many new cases of Ax or tetraploid species. In a 

 subsequent paper, Gates (20) has brought together a list of over 

 thirty cases of tetraploidy, natural or experimental, in plants and 

 animals. Tetraploidy is therefore a well recognized evolutionary 

 condition, and many new cases will doubtless be found when the 

 chromosome numbers of more plants are known. The gigantic 

 character of the cells in 0. gigas accounts for most, though 

 probably not all, the peculiarities of this mutant. 



The manner of origin of the tetraploid condition becomes, 

 therefore, a matter of much interest. In addition to the view 

 expressed by Gates and afterwards by Strasburger, Stomps (28) and 

 Miss Lutz (27) have suggested another method, namely that tetra- 



