652 Geological Periods of Mutation. 



of tlie best authorities; and shall not propose ?ny new 

 hypotheses, but merely point out the agreement between 

 the doctrine of mutation and the theories which have 

 been ])ut forward by others. I shall be treading new 

 ground and shall therefore be as brief as possible, refer- 

 ring the reader to the literature on the subject for in- 

 formation on special points without dealing with these 

 in detail. 



I will first discuss the conclusions which may be de- 

 rived from a consideration of the mutation period in 

 Oenothera Lamar ckiana, and shall then attempt to show 

 that these are in perfect harmony with geological and 

 paleontological facts. 



Starting from the fact that our Oenothera is at pres- 

 ent in a condition of mutability, we naturally ask the 

 question whether this condition has had a beginning or 

 not. If it had, the plant must have had, at some pre- 

 vious time, immutable ancestors; if it had not, all its 

 ancestors, back to the most simple organisms, were as 

 mutable as it is now. 



The former view agrees with that which was held 

 about tlie middle of the previous century, before the 

 spread of Dar wind's ideas. The general conception was, 

 *Vjue les especes varieraient plus a certaines epoques de 

 leur existence qu'a d'autres."^ This obviously leads, 

 in our special instance, to the supposition of a period of 

 mutation ; and this is exactly the view expressed in the 

 first volume of this book. It leads, further, to assume 

 periodic mutations which have alternated with periods of 

 immutability: for if all the various elementary characters 

 whose accumulation has ultimately led to the origin of 



^ H. Lecoo. Geographic hotauique, 1854. See also Alph. de Can- 

 DOLLE, Geographic hotauique raisonnee, II, pp. 1100-1102. 



