EXPERIMENTAL EVOLUTION 



529 



When discontinuous variation proceeds along a definite 

 line through several successive generations, each step being 

 an intensification of the preceding one, it is designated 

 ^' or tho genetic saltation^' (^ig- 395)- 



461. Illustration of the Pendulum.— The difference be- 

 tween discontinuous and fluctuating variation may be 



V..,/.s,,^ Fluciuatin^ 

 Extreme 



^■2^ F/uUuatn 

 Extreme c 



r- Mean 



Extreme 



Meo-n 



Fig. 396. — Diagram to illustrate the difference between fluctuating 

 variation and mutation; 0, original point of suspension; M, new point of 

 suspension after the mutation has occurred. 



aptly illustrated by a swinging pendulum (Fig. 396). The 

 vertical position, assumed when at rest, is the mean of all 

 positions that may be assumed as the pendulum swings; 

 34 



