KNOWLEDGE OF THE MUTATING OENOTHEEAS. 61 



explanation of the twin hybrids of DeVries is to be found in a fundamental alterna- 

 tiv^e dimorphic condition present in many of the wild forms. It is further probable, as 

 Honing thinks, that 0. Zamarckiafia and O. 7'ubrinervis are twin types corresponding 

 to the broad- and narrow-leaved forms. 



Several years' cultures from a colony of Oenotheras naturalized on the coast of 

 Lancashire near Birkenhead has shown that not only 0. LamarcMana and several of 

 its mutants (as previously known), but also 0. grandifiora and a host of other races 

 previously unknown, occur in this locality. Many of the latter races have been isolated 

 and several of them are found to breed true. Their bud characters are usually more or 

 less intermediate between 0. LamarcMana and O. gi^andijlora, which indicates their 

 hybrid origin. But they show the important fact that in Oenothera^ hybrid races 

 frequently form blends which breed true. Some of these races exhibit quite unex- 

 pected characters, and it remains to be determined whether a mutation factor in addition 

 to hybridization is necessary to account for some of them — i. e.^ whether, as in the case 

 of 0. Zamarchiana and its mutants, the characters of some of the races can not have 

 originated merely through hybrid blending and splitting. 



Numerous cultures of Oenotheras from Botanic Gardens, as well as data from other 

 sources, have shown that the line of distinction between the large-flowered, long-styled 

 and the small-flowered, short-styled forms is by no means so sharp as was formerly 

 supposed. In certain large-flowered races which have undergone crossing the style may 

 range from long to short in different flowers of the same plant. Wild species are also 

 known having large flowers and short style, and others having small flowers with long 



L 



style. There are in reality not merely two but a number of different lengths of style, 

 ranging from long, as in 0. grandifiora or 0. LamarcJcianay to very short, as in 



O. h7'emstylis. And in each species or race there is usually a narrow range of fluctua- 

 tion in length, which occasionally (apparently always in forms that have been crossed) 



becomes a remarkably wide range. 



Oenothera hybrids show a variety of types of behaviour, depending upon the relation- 

 ships of the forms concerned. Both blending and segregating types of inheritance occur, 

 the former nsually in interspecific crosses (though O. gigas shows tliis type of behaviour 

 in some cases), and the latter -usually in crosses between the mutants. Occasional 

 mutants — e. g., O. hrevistylis and O. rubricalyx — behave in typical Mendelian fashion. 

 The twin hybrids, first described by DeYries and here illustrated for the first time, 

 are produced when 0. biennis and certain other species are pollinated by O. Za- 

 marckiana or one of its derivatives. They are respectively broad- and narrow-leaved, and 

 are called laeta and velutina. The velutina type crossed back with Zamarckiana gives 

 velutina, laeta, and ZamarcUa/na in about the proportion 6:1:1. The twin types are, 

 so far as known, intermediate between the parents in flower-characters, but divergent 

 from either parent in leaf-characters. When self -pollinated they breed true, though it 

 has been shown by DeVries that they produce two kinds of pollen-grains or egg-cells. 



This type of inheritance, in which new, blended characters arise and breed true, occurs 

 also in numerous interspecific and interracial crosses in Oenothera^ and is probably of 

 fundamental significance in connection with the origin of new races. 



