OENOTHERA LAMARCKIANA MUT. VELUTINA. 161 



The question whether the characters of mutants and of hybrids 

 among the Oenotheras are single or built up of a less or greater 

 number of theoretically independent units now seems to be one of 

 principal interest to me. Until now, however, the analysis of the 

 qualities of the twin hybrids laeta and velutina has been difficult 

 and unreliable on account of the presence of the hereditary qualities 

 of their other parent. We can make inferences from these by com- 

 paring the twins issued from the crosses of different species with 

 0. Lamar ckiana, but we can hardly expect to get a complete analysis 

 in this way. The mutant velutina is free from these specific admix- 

 tures, and therefore may afford a better material for experiments 

 in this direction. I intend to study it from this point of view by 

 means of a number of crosses, most of which I made during the 

 summer of 1915, and shall give here only a description of the mutant 

 itself, and of those hybridizations which give proof of its right to 

 the name of velutina. 



In order to avoid confusion which might easily arise from the 

 similarity of the names 0. Lamarckiana hyb. velutina and 0. La- 

 marckiana mut. velutina, I will give a synonym to the latter and 

 call it 0. Lamarckiana mut. blandina, or briefly 0. blandina. In 

 descriptions the use of this latter term will be obviously easier. 

 0. blandina has throughout its life and in all its organs a paler tinge 

 than 0. Lamarckiana. 



0. blandina is, in all respects and at every stage of its evolution, 

 strikingly different from 0. Lamarckiana and easily recognizable. 

 Its marks become visible with its very first leaves, when still in the 

 seed pans, about 4—6 weeks after sowing. At the time when the 

 seedlings must be planted in larger boxes, their marks are fully 

 reliable, even in hybrid mixtures. Their leaves are narrow and a 

 pale yellowish green, whereas those of 0. Lamarckiana are broad 

 and a deeper green. As the rosettes increase the number and the 

 size of their leaves, the differences between the two types are seen 

 to increase also, and after some weeks more, when the young plants 

 are ripe for transplanting into the garden, 0. blandina is clearly 

 a type of its own and can easily be counted off in the mixtures. 

 In May the rosettes of 0. Lamarckiana gradually become very stout, 

 but those of 0. blandina remain slender. The leaves are so narrow 

 as not to touch each other regularly nor to cover the ground between 

 them. They resemble those of 0. rubrinervis, but lack the brittleness, 

 the typical bending of the petiole and blade, and the specific color 

 of this form. Moreover, they show a high degree of fluctuating 



ii 



