Parallel Mutations. 43 



CHAPTER V. 

 PA i< A 1. 1. K i. MUTATIONS. 



For many years (E. laniarckiana was the only CEnothera known 

 to exhibit mutations. Then mutations were discovered in a 

 race of (E. biennis, one of which showed all the peculiarities of 

 lata, but had the small flowers and other specific features of biennis. 

 From this form the conception of parallel mutations and the 

 recognition of their significance originated (see Gates, 1912a). 

 Shortly afterwards Stomps (1912a) described independently the 

 mutants nanella and semigigas from hybrids between (E. biennis 

 and CE. biennis leptomeres Bartl. (=(E. biennis crucitita de V.) but 

 apparently without recognizing the significance of their parallelism 

 to forms derived from laniarckiana. (E. biennis mut. lata was 

 later 1 described in detail and shown to have 15 chromosomes. It 

 was clear that the same kind of germinal change was involved in 

 both species. Two other probable mutations in (E. biennis, one 

 a red-nerved form parallel to rubrinervis Gates, the other 

 resembling Icevifolia, were also obtained. On these results the 

 conception of parallel mutations was founded, and it has since 

 been generally adopted by mutationists (see Stomps 1914, de Vries 

 1915b). 



Equally striking mutations have now been obtained from 

 several species of CEnothera, including such wild species as CE. 

 grandiflora, CE. stenomeres and (E. pratincola. In the last two 

 species, some of the mutations are parallel to those described in 

 CE. lamarckiana or CE. biennis t others are entirely dissimilar. A 

 number of cases of clearly parallel mutations are put together in 

 Table II, but a great many cannot readily be arranged in a table, 

 and these will be discussed separately. From the table it will 

 appear that three species have produced lata mutations (with 15 

 chromosomes), while five have produced mut. gigas (28 

 chromosomes) or mut. semigigas (21), and the same five species have 

 given rise to dwarfs. These mutations have also occurred in 

 various crosses. Virescence has also appeared independently in 

 three species of OEnothera. 



Let us now consider the history of some of these mutations, 

 especially in CE. biennis Linn., (E. stenomeres Bartl. and (E. 

 pratincola Bartl., all of which have small flowers, are self-pollinated 

 and rarely undergo natural crossing. The writer (1912, 1914) 



1 Gates & Thomas 1914. 



