DE VRIES'S ANALYSIS OF VARIATION 95 



" The systematic species," De Vries says, " are the practical 

 units of the systematists and florists, and all friends of wild 

 nature should do their utmost to preserve them as Linnaeus 

 has proposed them. These units, however, are not really 

 existing entities ; they have as little claim to be regarded as 

 such as the genera and families have. The real units are the 

 elementary species ; their limits often apparently overlap, and 

 can only in rare cases be determined on the sole ground of 

 field-observations. Pedigree-culture is the method required, 

 and any form which remains constant and distinct from its 

 allies in the garden is to be considered as an elementary species" 

 (1905, p. 12). 



Elementary species are considered to have originated from 

 their parent form in a progressive way ; they have succeeded 

 in attaining something quite new for themselves. 



Retrograde Varieties. — De Vries applies this term to those 

 numerous forms which have thrown off some peculiarity charac- 

 teristic of their ancestors. Like elementary species they may 

 arise suddenly, but while "progressive steps are the marks of 

 elementary species, retrograde varieties are distinguished by 

 apparent losses." Retrograde varieties usually differ from their 

 parent species by a single sharp character only, — they have 

 lost pigment, or hairs, or spines, and so on ; while elementary 

 species are distinguished from their nearest allies in almost 

 all organs. Moreover, the same kind of retrograde variety 

 occurs repeatedly in different series of species, hence the long 

 lists of unrelated varieties called by the same varietal title — e.g. 

 alba, inermis, canescens, or glabra. 



" Varieties differ from elementary species in that they do not 

 possess anything really new. They originate for the greater 

 part in a negative way, by the apparent loss of some quality, 

 and rarely in a positive manner by acquiring a character akeady 

 seen in allied species " (1905, p. 152). 



Ever- sporting Varieties. — De Vries uses this term to describe 



