MUTATIONS OF OENOTHERA SUAVEOLENS DESF. 



Besides Oenothera Lamarckiaiia there are quite a number of other 

 species of the Onagra group, which exhibit analogous phenomena of 

 mutability more or less frequently. The condition of Oe. Lamarckiana 

 is thereby shown not to be an isolated one, as was formerly believed. 

 All attempts to explain the mutations in this group by means of 

 qualities observed in or assumed for this main species have now to 

 be abandoned, unless they hold good for the explanation of the 

 whole range of new facts. Such is especially the case for the views 

 of those authors, who, by means of numerous unproven auxiliary 

 hypotheses, try to compress the large group of the phenomena of 

 mutation into the narrow limits of Mendelian segregation. 



Considered from a broad point of view some mutations are pa- 

 rallel ones, recurring in two or more different species, whereas 

 others are special for one type only. Of course, the parallel mutations 

 claim a prominent place in our theoretical considerations. Among 

 them the gigas type is generally described as a progressive change, 

 on account of the doubling of the number of its chromosomes. It 

 has sprung from Oe. Lamarckiana first, it arose of late in the cultures 

 of Bartlett among Oe. stenomeres and Oe. Reynoldsii and a very 

 beautiful Oe. grandiflora mut. gigas with 28 chromosomes was ob- 

 served in 1915 in my garden. Moreover Oe. biennis is known to mutate 

 in the same direction, giving Oe. biennis mut. semi-gigas 1 ). No wild 

 species of Onagra with 28 chromosomes is known, and no serious 

 attempt to explain this character on the ground of Mendelian 

 splitting has as yet been made. The claim that the doubling of 

 chromosomes observed in numerous other genera may have occurred 

 in nature after the same sudden manner as in the experiments of 

 Bartlett and myself, cannot be dismissed. 



Other parallel mutations are of a retrogressive nature and due 

 to the loss or latency of some character, which is active in the parent 

 species. The dwarfs of Oe. Lamarckiana, Oe. biennis and Oe. Rey- 

 noldsii give the best known instances. It seems fully evident that 



*) The literature on parallel mutations has been reviewed in my article on the 

 endemic plants of Ceylon and the mutating Oenotheras. Opera VII, p. 36. 



