352 Origin of Each Species Considered Separately. 



The proportion of albida mutants varies between 

 0.05 % and 9 %. 



This variabihty is also exhibited though to a con- 

 siderably less extent by the proportions in whicli O. al- 

 bida occurs among the offspring of various crosses. 



INDIVIDUALS OF OENOTHERA ALBIDA WHICH HAVE 



ARISEN BY MUTATION. 



II 



FROM CROSSES. 

 CROSS DATE TOTAL O. ALBIDA % ALBIDA 



O. Lamarckiana X O. nanella 

 O. lata X O. nanella . 

 O. lata X O. rubrinervis . 

 O. lata X O. scintillans . 

 O. scUitillans X O. nanella 

 O. lata X O. suaveolens . 



The mutants obtained in these two series of experi- 

 ments amounted to 472 and agreed in all their charac- 

 ters so far as these could be investigated. 



Flowering plants of 0. albida can be distinguished 

 from all other subspecies of O. Lamarckiana and from 

 this species itself just as easily as the seedlings and 

 rosettes can. They do not attain even in late autumn 

 a height of more than one meter; but as a rule they 

 give rise, about the middle of their stem to a group of 

 flowering branches, in the same way that O. rubrinerzns 

 does. Their leaves are narrow (Fig. SAA, p. 295), 

 pointed and very uneven; the crumples in them being 

 more numerous and more pronounced than in the parent 

 species (Fig. 57, transverse section of a leaf, see p. 310). 



The flowers are always somewhat smaller than those 

 of Lamarckiana, as would be expected from, a greater 

 delicacy of the species ; moreover they have a tendency 



