96 HEREDITY AND VARIATION 



qualities, but not really changing their nature. They are not 

 observed to produce anything quite new ; they always oscillate 

 around an average, and if removed from this for a time, they 

 show a tendency to return to it." They are inadequate ever to 

 make a single step along the great lines of evolution, whether 

 progressively or retrogressively. They do not form the raw 

 material of evolution, as* has often been supposed. But, we 

 submit, it is difficult with our present knowledge to discriminate 

 between a fairly large fluctuation and a small mutation. 



Mutations. " In contrast to the ever-recurring variability, 

 never absent in any large group of individuals, and determining 

 the differences which are always to be seen between parents and 

 their children, or between the children themselves, we have to 

 rank the so-called sports or single varieties, not rarely denomin- 

 ated spontaneous variations, for which I propose to use the term 

 ' mutations.' They are of very rare occurrence, and are to be 

 considered as sudden and definite steps " (1905, pp. 190-1). 



" De Vries recalls Galton's apt comparison between variability 

 and a polyhedron which can roll from one face to another. When 

 it comes to rest on any particular face, it is in stable equilibrium. 

 Small vibrations or disturbances may make it oscillate, but it 

 returns always to the same face. These oscillations are like the 

 fluctuating variations. A greater disturbance may cause the 

 polyhedron to roll over on to a new face, where it comes to rest 

 again, only showing the ever-present fluctuations around its new 

 centre. The new positio'n corresponds to a mutation " (T. H. 

 Morgan, 1903, p. 289). 



According to De Vries, mutations have furnished the material 

 for the process of evolution. 



The Oldest Known Mutation. A few years before the close 

 of the sixteenth century (1590), 'rprenger, an apothecary of 

 Heidelberg, found in his garden a pecufiar form of Chelidonium 

 majus or greater celandine. It was marked by having its leaves 

 cut into narrow lobes with almost linear tips, and by having the 



