The Making of Species 



acquisition of entirely new characters, and the 

 latter by the loss of existing qualities, or by the 

 gain of such peculiarities as may already be seen 

 in other allied species. If we suppose elementary 

 species and varieties originated by sudden leaps 

 and bounds, or mutations, then the elementary 

 species have mutated in the line of progression, 

 some varieties have mutated in the line of retro- 

 gression, while others have diverged from the 

 parental types in a line of digression or in the 

 way of repetition. . . . The system (of the vege- 

 table kingdom) is built up of species ; varieties 

 are only local and lateral, never of real import- 

 ance for the whole structure." 



De Vries asserts that these elementary species, 

 when once they arise, breed true, and show little 

 or no tendency to revert to the ancestral form. 

 We can, says De Vries, ascertain only by experi- 

 ment which plants are in the mutating state and 

 which are not. The great majority, however, are 

 not at present in the mutating state. 



The distinction between fluctuating variation 

 and mutation has been roughly illustrated by the 

 case of a solid block of wood having a number of 

 facets, on one of which it stands. If the block 

 be tilted slightly it will, when the force that has 

 tilted it is removed, return to its old position. 

 Such a gentle tilt may be compared to a fluctu- 

 ating variation in an organism. If, however, the 

 block be tilted to such an angle that when left to 



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