Retrograde Varieties 125 



verna, H elianthemum or of Taraxacum; all 

 characters are almost equally concerned. The 

 elementary species of Draba are characterized, 

 as we have seen, by the forms and the hairiness 

 of the leaves, the number and height of the 

 flower-stalks, the breadth and incision of the 

 petals, the forms of the fruits, and so on. 

 Every one of the two hundred forms included 

 in this collective species has its own tj^e, which 

 it is impossible to express by a single term. 

 Their names are chosen arbitrarily. Quite the 

 contrary is the case with most of the varieties, 

 for which one word ordinarily suffices to ex- 

 press the whole difference. 



White varieties of species with red or blue 

 flowers are the most common instances. If the 

 species has a compound color and if only one 

 of the constituents is lost, partially colored 

 types arise as in AgrostemmaCoronariabicolor. 

 Or the spots may disappear and the color be- 

 come uniform as in Gentiana punctata concolor 

 and the spotless Arum or Arum maculatum im- 

 maculatum. Absence of hairs produces forms 

 as Biscutella Icevigata glabra; lack of prickles 

 gives the varieties known as inermis, as for in- 

 stance. Ranunculus arvensis inermis. Cytisus 

 prostratus has a variety ciliata, and Solanum 

 Dulcamara, or the bitter-sweet, has a va- 

 riety called tomentosum. The curious mon- 



