334 Origin of Each Species Considered Separately, 



whilst in 0. nihrinervis the red stripes are handsome and 

 striking. 



To turn now to the general structure of the plant; 

 it has a greater tendency to develop lateral branches 

 from the main stem and, in connection with this fact 

 doubtless, fewer from the rosette (compare Figs, 49 and 

 67 with Fig. 55). But this feature is greatly affected 

 by the manner of cultivation. 



Fig. 69. Oenothera ruhrinervis. A, Transverse section of 

 the stem ; m. pith ; p, inner phloem ; h, wood ; b, bast bun- 

 dles between the outer phloem and the bark ; B, part of 

 such a bundle highly magnified; C, the same of O. La- 

 mar ckiana. 



This form can be distinguished at some little distance, 

 from the common Evening Primrose by the general habit 

 of its inflorescence and flowers ; but it is very difhcult to 

 find differentiating characters which can be described. 

 Plate I might, if it did not lack red pigment, pass as well 

 for a ruhrinervis as a Lamarckiana (see Fig. 43, p. 232). 



The whitish gray color, which is seen in a more pro- 

 nounced state in O. alhida, is not really due, as it appears 

 to be, to the greater hairiness of the plant ; but is brought 

 about by the swollen surfaces of the cells of the epidermis 



