No. 509] THE CATEGORIES OF VARIATION 263 



ization may be correlated with pronounced differences 

 in a single part. 



Among the forms arising by mutation from (Enofhera 

 lamarckiana De Vries distinguishes three varieties, 

 lavifolia, brevistylis and nanella. These forms are called 

 varieties instead of elementary species because they dif- 

 fer from the type in a few characters only and because 

 of their different behavior when crossed. But even ac- 

 cording to De Vries ' own description the points of differ- 

 ence are not limited to a single character. Lcevifolia, for 

 instance, is 



chiefly distinguished from Lamarck's evening primrose by its smooth 

 leaves, as its name indicates. The leaves of the original form show 

 numerous sinuosities in the blades, not at the edge, but anywhere be- 

 tween the veins. The blade shows numbers of convexities on either 

 surface, the whole under surface being undulated in this manner. It 

 lacks the brightness of the ordinary evening-primrose or (Enothera 

 biennis. These undulations are lacking or at least very rare on the 

 leaves of the new Icevi folia. Ordinarily they are wholly wanting, but 

 at times single leaves with slight manifestations of this character may 

 make their appearance. They warn us that the capacity for such 

 sinuosities is not wholly lost, but only lies dormant in the new variety. 



The leaves of Icevifolia are also ' ' a little narrower and 

 more slender than those of the Lamarckiana." But 

 Icevifolia also shows differences in the flower. "The 

 yellow color is paler and the petals are smoother. Later 

 in the fall, on the weaker side branches these differences 

 increase. The Icevifolia petals become smaller and are 

 devoid of the emargination at the apex, becoming ovate 

 instead of obcordate." 



Brevistylis is characterized by its short style. The 

 stigma is different in shape from that of the parent form ; 

 there are differences in the ovaries, and there are only 

 a few seeds produced. These differences maj possibly 

 depend upon a single varying character, although 



the leaves of the 0. brevistylis are more rounded at the tip, but the 

 difference is only pronounced at times slightly in the adult rosettes; but 

 more clearly on the growing summit of the stems and bitches. By 

 this character the plants may be discerned among the others, some 

 weeks before the flowers begin to show themselves. 



