ELEMENTARY SPECIES 75 



species. The same thing may be observed in the case of 

 violets; many distinct varieties or elementary species may 

 be recognized within the commonly recognized species, and 

 experiment has shown that these breed true. 



Among cultivated plants a similar diversity of forms oc- 

 curs, especially among such as are self -fertilized, as for 

 example wheat, beans and peas. Varieties differ in shape of 

 leaf, hairiness, color of seed, fruit or flowers, and many other 

 characteristics. Varieties of the same species may in many 

 cases be grown together in the same field without mixing, 

 and even if artificially crossed may not produce an inter- 

 mediate character but one which is distinctive of one parent 

 or the other. The same thing is true of our domesticated 

 animals. Varieties are often discontinuous, intermediates 

 being unknown. De Vries joins with Bateson in urging a dis- 

 continuous origin for such variations and brings forward 

 much experimental evidence in support of this idea. He 

 supposes that discontinuous variations arise through internal 

 causes, that is by mutation. 



2. " Mutation " in Oenothera. For proof of discontinuity 

 in variation De Vries relies principally upon a specific case 

 which he has studied for many years, that of Lamarck's 

 evening primrose {Oenothera Lamarckiana) . See Figs. 15-26. 

 This plant is supposed to be of American origin. It is culti- 

 vated in Europe (and to some extent in America) in parks 

 and gardens, for its showy yellow flowers. Here and there it 

 has escaped from cultivation and grows wild. In this condi- 

 tion De Vries found it in an abandoned potato field near 

 Amsterdam. But the plant has not been found growing wild 

 in the western hemisphere, original home of the Oenotheras. 

 For this reason some naturalists are inclined to regard it as 

 of hybrid and old-world origin. 



The plant is a biennial, five or six feet high when fully 

 grown, with a stout branching stem bearing at the ends of its 

 branches spikes of bright yellow flowers. They open towards 

 evening, as the name, evening primrose, indicates and are 

 polHnated by bees and moths. On bright days their duration 



