The Origin of Linaria J^ulgaris Pcloria. 219 



plants. Lastly the mutation in Linaria does not appear 

 along with others in space and time, but occasionally, 

 and scattered perhaps over the whole area of the parent 

 form and probably over the whole period of the life of 

 this race. 



The mutations of Oenothera Laniarekiana necessi- 

 tated the assumption of a definite premutation, but the 

 origin of the Peloria is obviously a phenomenon of a 

 different kind. 



Peloria is often regarded as an instance of atavism.^ 

 The c(^rrectness of this interpretation obviously depends 

 primarily on whether this term is used in a narrow or a 

 broad sense. Atavism is a reversion to ancestral char- 

 acters ; in the narrow sense to the complete type of par- 

 ticular ancestors, in the wider it refers only to single 

 characters. But it is clear that the spurs which form 

 a distinctive character of the genus Linaria must be older 

 than the species L. vulgaris, which cannot therefore have 

 had ancestors without the spur but with the other char- 

 acters of the species; so that L. vulgaris aneetaria can 

 occupy no place in the series of ancestors. The sym- 

 metry is ever so much older and L. vulgaris with regular 

 flowers has certainly never existed amongst the ancestors 

 of the common toadflax. Moreover the sterilitv of the 

 peloric plants does not favor such a view. 



If the Peloria must be regarded as atavistic, this view 

 can mean no more than the assertion that it has arisen 

 by the loss or latency of a character of the common 

 Linaria. Therefore we are concerned here with a retro- 

 gressive mutation, and the question arises, how far the 

 difi^erences between this case and the progressive muta- 

 tions with which we have become familiar in Oenothera 



* See L. JosT, Biolog. Cenfralbl, 1899. p. 149. 



