652 Geological Periods of Mutation. 
of the best authorities; and shall not propose any new 
hypotheses, but merely point out the agreement between 
the doctrine of mutation and the theories which have 
been put 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 Lamarckiana, 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 the middle of the previous century, before the 
spread of DARWIN'S ideas. The general conception was, 
"que les especes varieraient plus a certaines epoques de 
leur existence qu'a d'autres." 1 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 elementarv characters 
/ 
whose accumulation has ultimately led to the origin of 
1 H. LECOO, Geographic botauique, 1854. See also ALPH. DE CAN- 
DOLLE, Geographic botaniquc raisonnce, II, pp. 1100-1102. 
