RETROGRESSIVE VARIETIES 135 



constellations. But the species may also include " varieties," 

 more or less sharply distinguished from the rest of the species by 

 the apparent absence of some notable specific feature, or, more 

 rarely, by the acquisition of some peculiarity already seen in 

 closely allied species. They stand aside, as it were, like far out- 

 lying parts of the constellation. " Varieties," thus defined, 

 usually differ from their parent species in a single sharp character 

 only, or in several correlated characters ; they usually arise in 

 a negative way by the apparent loss of some quality ; and they 

 have great stability. They are comparable to the familiar colour- 

 varieties in rabbits, guinea-pigs, mice, etc., which seem to arise 

 by the dropping out of part of the ancestral equipment of char- 

 acters. They are in no sense reversions. 



Illustrations. 



White " varieties " of red and blue flowers e.g. of red-flowering 

 currant. 



Smooth " varieties " of hairy plants e.g. nectarine (from peach). 



Smooth "varieties " of prickly plants e.g. holly and gooseberry. 



Rayless "varieties" of many composites normally with ray 

 florets e.g. white marigold, camomile, daisy. 



Radiate " varieties " of many composites, normally with no 

 ray-florets e.g. tansy and groundsel. 



Red "varieties " of white flowers e.g. hawthorn. 



Red " varieties " of green trees and shrubs e.g. beech and birch. 



Weeping " varieties " of ash, willow, etc. 



Starchless seeds e.g. sugar-corn. 



Seedless fruits e.g. banana and mandarin orange. 



Mr. Burbank's stoneless plum. 



As these varieties are most frequently in a negative direction 

 having apparently lost some character which their parent-species 

 possesses, De Vries includes most of them in the term "retrograde 

 varieties." Perhaps "retrogressive varieties " would be a clearer 

 term. 



They usually breed true, but some of them are perpetuated 

 asexually e.g. of course, the seedless fruits. Sometimes, 

 however, the apparently lost ancestral character re-appears, as 

 when the smooth nectarine, a " variety " of peach, becomes 



