species in Nature. 173 



together over 50 species of Draba verna^ in his garden,^ 

 and from other countries in Europe, especially from Eng- 

 land, Italy and Austria, about 150 more, so that in 1873 

 he had more than 200 forms in cultivation.^ 



This richness in forms, or polymorphism as it is 

 called, of the so-called *'good" species is quite a general 

 phenomenon.^ Darwin repeatedly called attention to 

 it and argued that as a result of it the most widely dis- 

 tributed types had the best chance of giving rise to new 

 species and so of gradually becoming genera. •"* In the 

 case of rare forms he showed the prospect of doing so 

 to be much smaller. 



Very few plants are as rich in subspecies as Draba 

 verna. Perhaps Viola tricolor comes next^ with its 

 well-known subspecies Viola arvensis which is itself 

 a collective form.'^ In Germany or France the average 

 number of subspecies per species may be placed at 2 or 3, 

 for the whole of Europe the average is perhaps about 10. 

 If all these forms were noted and described the Flora of 

 Europe would be increased tenfold, which would be most 

 inconvenient. But just as there are valuable treatises 

 which only deal with the genera or at any rate only with 

 these and their more important species, so it would be 

 the business of the ordinary Floras to describe the species 

 and their more important subspecies. The task of deal- 



^ See Fig. 3 on page 22. 



^ Dc I'origine dcs arhrcs fniitiers, 1853. 



^ Dcs cspcces vcgetales, aiRnes, p. 13, 1873. 



*It is often spoken of as "Variability": but this cannot conceal 

 the fact that the elementary species which compose the species are 

 constant, and independent of one another. 



^ Wallace^ Darzuinism, p. 80 and 98. 



® A. Jordan, Observations snr plusieurs plantcs nouvelles, 1846- 

 1849, Vol. II, p. 7. 



"^ See Fig. 4 on page 23. 



