1^'* NOTICES OF BOOKS. 



These considerations lead M. de Candolle to a still more purely hy- 

 pothetical subject, viz. the greater variability of species in certain geo- 

 logical epochs or during certain epochs of the existence of the species. 



Against the idea that species are more variable at certain times than 

 at others, M. de Candolle urges that it is to revolutions of the earth's 

 surface that we must look for causes that would effect sudden changes 

 of species, and that these revolutions can only be exaggerations of 

 operations now in action, and which do not produce the slightest' 

 effect on the majority of existing species. 



M. Lecoq's theory, that species like individuals have a definite period 

 of development, followed by a stationary one, and that again by ex- 

 tinction, is opposed by M. de Candolle, firstly, on the ground that it 

 is unphilosophical to confound a complex with a simple phenomenon. 

 According to Isidore G. St. Hilaire and many other naturalists, the so- 

 called species of any epoch are all races derived from the fewer pre- 

 existing races ; and M. de Candolle considers the fact as proven, that a 

 race^ once established is itself very variable, citing the opinion of M. 

 Louis Vilmorin, who has shown satisfactorily that to produce a race 

 the constitution of the species operated upon must be shakeu {ebranlee, 

 affoUe), after which it becomes more amenable to the experimenter. 

 Now, according to Lecoq, newly created forms are more variable than 

 the same are at a later period, and those genera that contain a great 

 many indeterminable forms {Bosa, Salix, Viola, Folygonum, Thalidrum, 

 Euhus, etc.) may hence be assumed to be in a young or partially deve- 

 loped state.* These ideas are combated by M. de Candolle, who 

 shows that they are founded mainly on a preconceived idea of what 

 IS to be considered a species and what not; that, for example, the 

 botanist who sees only five or six distinct species of Rvbus, each of 



«,1.4„I .•_ _ • r. •• , , . ^ ' 



vanes 



I!n™" •''"'• ^°^ *' ^"^^^^^ ''^^^''''^ conditions are often seen sudJeulv to induce 

 Pnon^rr T'"^' f °:i!y. ^I'^f-tly altered conditions -produce equal chauies, if time 



M df rtn r- h °'*?'?' °P|'"*^""- <^^"* *^« fi^st «t<^P. sW the opponents of 

 JW.. de Landolle s hvnothpsis ami oiin„r +t,„ *■ i,-_ i- ,, ^ ' ,'^ •_ .„j 



formation 



n TPr,o+;t;..„ c .1. ■' i'" "*,;-?"' """ """" Lue lormanon ol the race or subspecies, ana 



duce'^a Spn,vf '=°°<i^t'°°« niay well ^ i„„ease the amount of change as to pro- 

 auce a species, a genus, and so forth. 



of *T,kn^r5 r! ""^'"P^^ ""J^ ^f'^'^^y '^«d to the conclusion that the majority 



of It1« Jif f' <^°es t«/a extent which few botanists have an adequate idea 

 these but Jlr'n ."'' °^- '^''*^'^*=^°^ ^*=tween single herbarium specimens of 

 ^ner; become Tnr^.''"'' '""T^ ^^^ Previously well-defined spec es of large 

 '^Z.i7^::Z.tlt7Jt'^' "' ^-"--tion by the iEtercalation of 



