Elementary Species in Nature 49 



ways. All in all there are constant differences 

 which are so great that it has been possible to 

 distinguish and to describe large numbers of 

 types. 



Many of them have been tested as to their 

 constancy from seed. Jordan made numerous 

 cultures, some of which lasted ten or twelve 

 years; Thuret has verified the assertion con- 

 cerning their constancy by cultures extending 

 over seven years in some instances ; Villars and 

 de Bary made numerous trials of shorter dura- 

 tion. All agree as to the main points. The local 

 races are uniform and come true from seed ; the 

 variability of the species is not of a fluctuating, 

 but of a pol}Tnorphous nature. A given ele- 

 mentary species keeps within its limits and can- 

 not vary beyond them, but the whole group 

 gives the impression of variability by its wide 

 range of distinct, but nearly allied forms. 



The geographic distribution of these ele- 

 mentary species of the whitlow-grass is quite 

 distinct from that of the violets. Here predom- 

 inant species are limited to restricted locali- 

 ties. Most of them occupy one or more depart- 

 ments of France, and in Holland two of them 

 are spread over several provinces. An import- 

 ant number are native in the centre of Europe, 

 and from the vicinity of Lyons, Jordan suc- 

 ceeded in establishing about fifty elementary 



