162 OENOTHERA LAMARCKIANA MUT. VELUTINA. 



variability in their color. This is always gray, on account of the 

 hairiness of the surface, but it varies between a normal green and 

 a more or less pale and yellowish tinge. The paler they are, the 

 poorer they are in chlorophyll, and therefore the palest individuals 

 soon begin to show a slower growth. They stay behind the others 

 the more, the paler they are. These differences increase if the culture 

 is densely planted, and even at the time of flowering the paler in- 

 dividuals may be seen to be much weaker and shorter than the 

 others. In ordinary cultures, however, when the plants are at a 

 distance of 20 cm. or more from their next neighbors, and grown 

 in a well manured soil, these differences gradually disappear and 

 are no longer visible when the first flowers open. In order to fertilize 

 pale individuals beside the green ones, I had to mark them in early 

 youth. From the self-fertilized seeds of the green ones the seedlings 

 are on the average less pale than those of the paler parents, but 

 the difference, although obvious and unmistakable on the beds in 

 springtime, soon disappears as the summer begins. From time to 

 time there is even a partial variability, such as, for instance, a green 

 branch on a stem with pale leaves. This shows that there is no 

 racial difference between the green individuals and the pale ones, 

 even as in the cases of Oenothera {Lamar ckiana x atrovirens) gracilis 

 and of 0. {Lamarckiana x Hookeri) velutina 1 ). Since making these 

 experiments (1912-1913) I have cultivated 0. blandina so as to reduce 

 the paleness of its leaves to the first youth of the rosettes, and to 

 have no diminution of the individual strength of my seed-bearing 

 specimens on account of it. 



At the time of flowering the plants are much more slender than 

 those of 0. Lamarckiana, and are in their main features very much 

 like the velutina hybrids of 0. biennis x Lamarckiana and of 0. 

 Lamarckiana x 0. biennis Chicago, and especially like the latter, 

 with which in some instances they can easily be confounded. The 

 leaves on the stem are narrow, reaching about two-thirds the breadth 

 of those of Lamarckiana if compared by equal length. In the begin- 

 ning they are folded along their midvein, but later they become 

 flattened, and this curious character may then be seen only in the 

 bracts of the inflorescence. The bubbles, which are so characteristic 

 of the leaf blades of 0. Lamarckiana, are absent in the mutant. 

 I shall designate this lack of bubbles by the term "smooth". 



*) Gruppenweise Artbildung. Berlin, 1913, p. 164, where O. atrovirens still 

 bears the name of O. cruciata (fig. 73); and p. 116, fig. 46, for the twin hybrids 

 of O. Hookeri. 



