14 Descent 



rily by the disappearance of some superficial 

 character that a variety is distinguished from 

 its species, as by the lack of color in the flowers, 

 of hairs on stems and foliage, of the spines and 

 thorns, &c. Such varieties are, strictly speak- 

 ing, not to be treated in the same way as elemen- 

 tary species, though they often are. We shall 

 designate them by the term of " retrograde 

 varieties, ' ' which clearly indicates the nature of 

 their relationship to the species from which they 

 are assumed to have sprung. In order to lay 

 more stress on the contrast between elementary 

 species and retrograde varieties, it should be 

 stated at once, that the first are considered to 

 have originated from their parent-form in a 

 progressive way. They have succeeded in at- 

 taining something quite new for themselves, 

 while retrograde varieties have only thrown 

 off some peculiarity, previously acquired by 

 their ancestors. 



The whole vegetable kingdom exhibits a con- 

 stant struggle between progression and retro- 

 gression. Of course, the great lines of the gen- 

 eral pedigree are due to progression, many 

 single steps in this direction leading together to 

 the great superiority of the flowering plants 

 over their cryptogamous ancestors. But pro- 

 gression is nearly always accompanied by re- 

 trogression in the principal lines of evolution, 



