62 Mutability and Individual Variation. 



TELEXES laws to these cases. For each character there is 

 a mean, around which the variants are grouped according 

 to the laws of probabihty. In similar fashion, the split- 

 ting of the leaves in Chclidoniiun laciniatwn, varies; 

 even glabrous and unarmed varieties exhibit a certain de- 

 gree of variability in the extent to which they manifest the 

 character which they are supposed not to possess. (Young 

 shoots of Bisciitclla laevigata glabra, fruits of Acs- 

 cnlus Hippocastaniun incrmis, and so forth.) Five leaved 

 clover {Trifoliiun pratcnse qiiinqiic folium) varies in the 

 number of leaflets between 3 and 7 , obviously following 

 Quetelet's laws.^ The characters peculiar to Papaver 

 soninifcruni polycephalum (Figs. 27 and 28, Chap. IV, 

 § 16) and Papaver bracteatiun monopetahim (Fig. 1, 

 p. 12) are in the highest degree variable. The same 

 is true of the syncotylous and tricotylous races. The 

 widest range of variability and complete immutability 

 are frequently associated.^ Such variation or fluctuation 

 is therefore an occurrence of quite a different order from 

 mutation. 



// § 6. THE MUTATION HYPOTHESIS. 



Although I do not intend to discuss the views of my 

 contemporaries on selection and mutation at large in this 

 work,^ I shall now call attention to the fact that ob- 

 jections are continually being raised against the theory 

 of selection from all sides. ^ The authors in question 



* Over het omkcercn van halve Galton-ciirven, Botanisch Jaar- 

 boek of the Society Dodonaea, X. Jahrg., 1878, p. 46. 



'Alimentation et Selection. Vol. Jubilaire de la Societc dc Bio- 

 logie de Paris, Dec. 1899. 



^ For a critical presentation of both sides of the question the 

 reader is referred to O. Hektvvig^ Zeit- und Streitfragen der Biologie. 



* See also Bateson, Materials, p. 567. 



