VARIATION AND HEREDITY 127 



Ordinary variation, which is also known as 

 individual, fluctuating or gradual variation, 

 is always present; and it can be described in 

 terms of perfectly definite laws which have 

 now been fairly completely formulated. It 

 provides the breeder with material for his 

 improved races. On the other hand, he has 

 to deal with mutations which do not need 

 repeated selection, but, at the most, must be 

 kept free from admixture, and which almost 

 always breed true from the first." 



In support of his theory, Professor de 

 Vries has relied mainly on the sudden and 

 repeated leaps and remarkable subsequent 

 constancy exhibited by the progeny of a 

 stock of evening primrose, (Enothera la- 

 marckiana, which he found growing in a wild 

 state near Hilversum in Holland. But many 

 other instances of mutation are adduced, the 

 oldest and most accurately described being 

 the origin of the cut-leaved variety of the 

 greater celandine, Chelidonium ma jus lacin- 

 iatum, which occurred suddenly in 1590 in 

 the garden of an apothecary at Heidelberg, 

 and has been constant ever since. The evi- 

 dence of mutations in the animal kingdom is 

 only beginning to be gathered, and there are 

 few satisfactory cases known outside of 

 experimental stations. There are, however, 

 many species, e.g, of birds, which differ from 



