322 Origin of Each Species Considered Separately. 



are obcordate and more or less deeply emarginate at their 

 broad apices. In both species the petals are about 3 cm. 

 long; but in O. Lamarchiana they are 5 cm. broad, whilst 

 in O. gigas they are 6 cm, 



I did not find any other differences worth mentioning 

 in the absolute or relative dimensions of the flowers. 

 The size of the flowers of both species gradually de- 

 creases as autumn comes on, a fact which must be borne 

 in mind when we are looking for constant differences 

 between the two. The same is true of the calyx tube and 

 of the tip of the calyx, of the height of the stigma and of 

 the anthers and so forth. Speaking broadly gigas is more 

 compact than Lamarckiana ; and though its flowers do not 

 exceed those of its parent species in number, they form a 

 denser and therefore more beautiful head on the stem. 



The fruits of 0. gigas are very different from those 

 of O Lamarckiana : they are half as long but about as 

 stout. The seeds are on this account less numerous; 

 but they are larger and heavier. 



Oenothera gigas is stronger than the other species in 

 almost every respect. This is seen most strikingly in 

 the girth of the stem as shown in Plates I and II and in 

 figures 60 and 61. The stem is stronger right from its 

 base, and for that reason grows more vertically upwards 

 — a feature which greatly facilitates the recognition of 

 the young plants. In the flowering region the diameter 

 of the stem is almost twice as large as it is in O. La- 

 marckiana, in which it is at most 5-6 mm. : in gigas it is 

 often 10 mm. 



The whole stem is much more thickly beset with 

 leaves and the leaves themselves are broader, more nu- 

 merous, and more or less recurved. The great number 

 of leaves is due to the shortness of the internodes ; in the 



