Progrcssk'c, Retrogressive, Degressive M ufufioiis. 571 



so we can imagine that a new character remains hitenl 

 for some time after its first origin, its phylogenelic birth, 

 if I may so express it, and does not become active until 

 after the lapse of a lesser or greater period of time. 



According to this view, every progressive mutation 

 is fundamentally a double process, and consists in the 

 production of a new internal factor and in its activation. 

 Both may sometimes happen at the same time, but this 

 is not necessary. It is therefore desirable to apply sepa- 

 rate names to the two processes : the internal one I have 

 called premutation, the externally visible one a mutation 

 seusu strieto. 



The premutation is therefore of a hypothetical, the 

 mutation, however, of an empirical nature. 



It further follows from this that an niternal factor 

 does not of itself lead to the origin of an external change. 

 As in ontogeny so also in phylogeny an elementary char- 

 acter can be sometimes active, but at other times latent 

 or inactive. If a new character emerges from its original 

 latent conditions and becomes active, we call the process 

 a progressive mutation ; conversely we can denote its 

 return from the active to the latent condition as a retro- 

 gressive mutation. 



The experience of gardeners and of the systematists 

 with the smaller species and varieties teaches that retn^- 

 gressive mutations of this kind are common phenomena. 

 Almost any character may disappear. This applies not 

 nnlv to the sunerficial characters, such as col(^r. hairs, or 

 thorns, but also to those deeper ones which affect the 

 inner organization of the plant, such as the decussate ar- 

 ran element of leaves, and even the svmmetrv of the origan- 

 ism. Spiral torsion and peloria show how i)rofound an 

 alteration in the appearance of a i^lant (-»r in the structure 



