240 SECRETS OF ANIMAL LIFE 
and less to fluctuations. (As for individually 
acquired modifications, imposed on the body from 
without, instead of emerging from the changeful 
germ-plasm within, they do not seem to be in 
themselves of much direct racial importance, for 
there is no cogent evidence of their transmissibility. ) 
Darwin knew, of course, of some of the transilient 
or saltatory variations, which are now called muta- 
tions, but he deliberately passed them by and laid 
emphasis on the selection of fluctuations. His 
strongest reason for so doing was his conviction 
that the sudden ‘single variations” or sports 
would be readily swamped or leveled down by 
inter-crossing. It is now known, however, that one 
of the characteristics of mutations is their capa- 
bility of complete inheritance in a varying percent- 
age of the progeny. 
To the Dutch botanist De Vries especial credit is 
due for his recognition of the evolutionary im- 
portance of mutations and for his study of their 
behavior in inheritance. It is an often-told story 
how he found, in 1886, in a potato-garden near 
Hilversum, in Holland, a race of the Evening Prim- 
rose, enothera lamarckiana, in which the mood was 
all mutation. In spite of Galton’s insistence on the 
reality of transilient variations and Bateson’s mar- 
shaling of instances of discontinuity, the tendency 
had grown strong to dogmatize about the con- 
tinuity of organic change, just as previously about 
the fixity of species. ‘‘ Natura non facit saltus,” 
they said; but De Vries discerned Natura saltatrix 
