THE MUTATION THEORY 105 



some which in botanic gardens pass for original species. Whether 

 actual wild plants from their native habitats are in the same 

 state, is not yet known, but it is by no means improbable. The 

 case may be compared with that of the moth Abraxas grossu- 

 lariata studied by Doncaster and Raynor, in which the females 

 are all heterozygous, or we may almost say "hybrids" of grossu- 

 lariata and the variety lacticolor. Similarly we may say that at 

 least garden Petunias are heterozygous in respect of singleness. 

 The proof of this is of course that when fertilised with the pollen 

 of doubles they throw a mixture of doubles and singles. The 

 statements which de Vries has published regarding the behaviour 

 of several of the Oenotheras go far to show that they must have 

 a somewhat similar organisation. On the present evidence it is 

 still quite impossible to construct a coherent scheme which will 

 represent all the phenomena in their interrelations, and among 

 the facts are several which, as will appear, seem mutually incom- 

 patible. The first indication that the Oenotheras may have 

 either mixed ovules or mixed pollen appears in the fact that 

 Lamarckiana and several of its "mutants" used as males, with 

 several other forms as females, give a mixed offspring. For 

 example, de Vries (1907) found that 



biennis 9 X Lamarckiana cf 



biennis cruciata 9 X Lamarckiana c? 



muricata 9 X Lamarckiana cf 



biennis 9 X rubrinervis c? 



biennis cruciata 9 X rubrinervis cf 



all give a mixture of two distinct types which he names laeta 

 and velutina, consisting of about equal numbers of each. On 

 account of the fact that the two forms are produced in association 

 de Vries has called these forms "twin hybrids," a designation 

 which is not fortunate, seeing that it is impossible to imagine 

 that any kind of twinning is concerned in their production. The 

 distinction between these two seems to be considerable, laeta 

 having leaves broader, bright green in colour, and flat, with 

 pollen scanty, while velutina has leaves narrower, grayish green, 

 more hairy, and furrow-shaped, with pollen abundant. 



We next meet the remarkable fact that these two forms, 



