92 NEW DIMORPHIC MUTANTS OF THE OENOTHERAS. 



leaves are clearly shorter, and the blade is set off from the narrowly- 

 winged petiole by a sharp indentation. This character causes the 

 rosettes to be more open because the petioles hardly touch one 

 another. 



This spatulate form of the leaves remains, for a long time, the 

 best mark of the race; but when the stem grows up, the whole 

 plants is much more slender than the parent form (fig. 3). The 

 stem is thin and low; in July, when the first flowers open, it often 

 reaches only 75 cm., when the corresponding specimens of Lamarcki- 

 ana are already 1 m. and more in height. After a time, however, 

 this difference disappears, since the spike is more elongated. It 

 is less dense than in Lamarckiana ; the bracts are much shorter and 

 strikingly broader; the flower buds are large and conical, the 

 flowers somewhat smaller, although still larger than those of 0. 

 biennis; the pollen is abundant and the fruits are short and thick, 

 containing a good supply of seed. The foliage is of the same green 

 color as in the parent form, but much more crinkled and uneven, 

 not as gray as in 0. cana, nor as hairy as in this form. 



The impossibility of distinguishing the young plants before 

 planting out evidently makes this mutant less fit for the determi- 

 nation of splitting percentages, because the sorting and counting 

 has to be done on the beds. In my experiments I have always 

 counted the individuals of the two types at the beginning of the 

 flowering period, since at this time the limits between the two 

 groups are the most sharp. 



Moreover, this similarity between the mutant and the parent 

 species must diminish the chances of discovering mutant specimens 

 of the new type. This is probably the reason why it was not observed 

 before 1911. Since that year new mutants of the pallescens type 

 have more than once arisen from 0. Lamarckiana and from some 

 of its derivatives, especially in 1914. All of these mutants exactly 

 resembled the first one in their whole structure and in all their 

 marks. 



I have made pedigree cultures of the offspring of my first three 

 mutants. These arose from seed of the same parent plant of 1909, 

 which belonged to the second generation of a guarded strain of 

 0. Lamarckiana, derived from a rosette collected in 1905 in the 

 original field near Hilversum. One part of this seed was sown in 

 1910 and yielded, among about 500 specimens, 1 pallescens, together 

 with 1 rubrinervis, 3 oblonga, 2 lata, 1 scintillans, 1 nanella, the 



