OENOTHERA LAMARCKIANA MUT. VELUTINA. 173 



of the mutation occurring very much smaller still. It is sufficient 

 to suppose that only the female elements of the original 0. laeta 

 have mutated in this way, although we cannot know whether this 

 change might not have taken place in the male cells. And since 

 0. blandina behaves as an isogamous species, both hypotheses seem 

 to be equally probable. In both cases mutants of the laeta type 

 should be expected to appear also, but as they would be very rare 

 and not discernible in the beginning from the Lamarckiana specimens 

 which always develop out of a part of the seeds of 0. lata, they 

 would surely have been overlooked in the years 1907—1908, when 

 the mutation into blandina occurred. 



I shall now give a more detailed description of my experiments. 

 The crosses were made in 1913 and the first generation was culti- 

 vated twice for every cross, once in 1914 and once in 1915. 



0. blandina x 0. Lamarckiana. — A biennial specimen of the 

 latter form was chosen and its pollen placed on the stigma of two 

 individuals of the thoroughly green type of 0. blandina. The seeds 

 of one cross were sown in 1914, and those of the other in 1915. 

 The first culture consisted of 23 laeta and 34 velutina, making a 

 total of 58, with 41 per cent laeta. In 1915 the figures were 46 laeta 

 and 39 velutina, or 54 per cent laeta in 85 specimens. Although the 

 size of the cultures was small, they evidently point to a division 

 in nearly equal groups. The two types were clearly different from 

 the beginning and could easily be counted out in June before the 

 production of the stems. In 1915 I separated them in March, at 

 the time of planting into the boxes, in order to control my estimate 

 later on, and in April planted the laeta in one group and the velutina 

 in another half of the bed. In 1914 I had 25 and the following year 

 10 flowering plants, half of which belonged in each case to the 

 laeta type and the other half to the velutina type. The laeta have 

 already been described; the velutina were in no respect and at no 

 time different from ordinary 0. blandina. 



The second generation from seed of one of the velutina plants 

 embraced 30 flowering and 40 younger specimens, all of which 

 exactly repeated the marks of their parent. From the seeds of one 

 self-fertilized laeta, however, I got the splitting group already 

 described. Its two types were the same as in the previous generation. 

 I recognized the splitting in the seed pan, but counted them only 

 in June after planting out 15 laeta and 15 velutina. All in all I had 

 80 plants, of which 26 were laeta and 54 velutina, or 33 per cent 

 laeta, which is somewhat less than in the first generation. All the 



