526 POPULAR SCIENCE MONTHLY. 



those humble places, will do a few days' weeding, prick out some rows 

 of cabbages, feed up a few score of any variable larva, he will not wait 

 long before he learns the truth about variation. If he go further and 

 breed two or three generations of almost any controllable form, he 

 will obtain immediately facts as to the course of heredity which obviate 

 the need for much laborious imagining. If strictly trained, with faith 

 in the omnipotence of selection, he will not proceed far before he en- 

 counters disquieting facts. Upon whatever character the attention be 

 fixed, whether size, number, form of the whole or of the parts, propor- 

 tion, distribution of differentiation, sexual characters, fertility, pre- 

 cocity or lateness, color, susceptibility to cold or to disease — in short, 

 all the kinds of characters which we think of as best exemplifying 

 specific difference, we are certain to find illustrations of the occurrence 

 of departures from normality, presenting exactly the same definiteness 

 elsewhere characteristic of normality itself. Again and again the cir- 

 cumstances of their occurrence render it impossible to suppose that 

 these striking differences are the product of continued selection, or, 

 indeed, that they represent the results of a gradual transformation of 

 any kind. Whenever by any collocation of favoring circumstance such 

 definite novelties possess a superior viability, supplanting their ' nor- 

 mal ' relatives, it is obvious that new types will be created. 



The earliest statement of this simple inference is, I believe, that 

 of Marchant,* who in 1719, commenting on certain plants of Mer- 

 curialis with laciniated and hair-like leaves, which for a time estab- 

 lished themselves in his garden, suggested that species may arise in like 

 manner. Though the same conclusion has appeared inevitable to 

 many, including authorities of very diverse experience, such as Hux- 

 ley, Virchow, F. Galton, it has been strenuously resisted by the bulk 

 of scientific opinion, especially in England. Lately, however, the be- 

 lief in mutation, as De Vries has taught us to call it, has made notable 

 progress,! owing to the publication of his splendid collection of obser- 

 vations and experiments, which must surely carry conviction of the 

 reality and abundance of mutation to the minds of all whose judg- 

 ments can be affected by evidence. 



That the dread test of natural selection must be passed by every 

 aspirant to existence, however brief, is a truism which needs no special 



* Marchant, Me"m. Ac. roy. des sci. for 1719; 1721, p. 59, Pis. 6-7. I owe 

 this reference to Coutagne, L'he'rddite' chez les vers a soie (Bull. sci. Fr. Belg., 

 1902). 



t This progress threatens to be rapid indeed. Since these lines were written 

 Professor Hubrecht, in an admirable exposition (Pop. Sci. Monthly, July, 

 1904) of De Vries's ' Mutations-theorie,' has even blamed me for having ten 

 years ago attached ani/ importance to continuous variation. Nevertheless, 

 when the unit of segregation is small, something mistakably like continuous 

 evolution must surely exist. (Cp. Johannsen, ' Ueb. Erblichkeit in Popu- 

 lationen und in reinen Linien,' 1903.) 



