Systematic Atavism 643 



for each stem and each branch, but as a rule, 

 the stronger axes are more liable to furnish 

 anomalies than the weaker. 



Exactly the same thing is true of double 

 adaptations. Every bud of the water-persi- 

 caria may develop either into an erect or into a 

 floating stem, according as it is surrounded by 

 water or by relatively dry soil. In other cases 

 utility is often less manifest, but some use may 

 either be proved, or shown to be very probable. 

 At all events the term adaptation includes the 

 idea of utility, and obviously useless contriv- 

 ances could hardly be brought under the same 

 head. 



We have also dealt with the question of 

 heredity. It is obvious that from the flowers of 

 the floating and erect stems of the water-persi- 

 caria seeds will result, each capable of yielding 

 both forms. Quite the same thing was the case 

 with the teasels. Some 40$ of the progeny pro- 

 duce beautifully twisted stems, but whether the 

 seed was saved from the most completely 

 twisted specimens or from the straight plants 

 of the race was of no importance. 



This phenomenon of twisting may now be 

 considered from quite another point of view. 

 It is a case of systematic atavism, or of the re- 

 acquirement of some ancient and long-lost qual- 

 ity. This quality is the alternate position of 



