Oenothera Scintiltans. 377 



of more than 10-15 centimeters. But even the common 

 Lamarckiana often produces some abnormal flowers 

 amongst the lower ones. If the nanella survives this pe- 

 riod and if it becomes markedly stronger it forms, first, 

 a shorter or longer intermediate piece and then a fine 

 head of large flowers. This is borne by the barren look- 

 ing, bracteated, flowerless part of the stem, well above 

 the lower half of the inflorescence. But it is by no means 

 all plants that are strong enough to reach this state. 



The best way of raising fine plants of nanella is to 

 make them biennial by sowing the seed late. 



C. THE INCONSTANT SPECIES. 



§ 19. OENOTHERA SCINTILLANS. 

 (Plate V.) 



As far as we know, species in nature are constant. 

 This is true also of elementary species, and of most so- 

 called varieties. It is true that the older systematists, 

 such as Koch, Spach and many others, believed to be 

 able to distinguish varieties from species by their in- 

 constancy. But they seldom took the trouble to exclude 

 the visits of insects in the numerous experiments they 

 made. If we take this precaution many varieties prove 

 to be as constant as species. 



The universal belief in the constancy of species has 

 led us to regard this quality as one of the attributes of 

 a species. From this standpoint, it would seem a con- 

 tradiction in terms to speak of an inconstant species. 



But such a contradiction need only trouble adherents 

 of the current theory of selection. The mutation theory 

 can remove even this difficulty. Lack of constancy is 



