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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