698 BRITTLE RACES OF OENOTHERA LAMARCKIANA. 



velutina gametes the factor for brittleness which is so characteristic 

 of 0. Lamar ckiana. 



Oenothera Lamarckiana scindens. 



This is a race which is externally like a pure Lamarckiana, but 

 produces only a very small amount of barren seeds. It originated 

 from a cross made in 1913 between my pure races of Lamarckiana 

 and rubrinervis. The seeds were sown in 1916, and yielded 32 per 

 cent Lamarckiana, 20 per cent lucida, and 48 per cent rubrinervis. 

 In this respect there was no deviation from the ordinary rule. Of 

 the Lamarckiana type, only three specimens were self-fertilized. 

 Two of them produced 66 and 75 per cent of empty seeds, as might 

 be expected. The third, however, had only 7 per cent of such seedlike 

 structures. From this it was evident that a new type had arisen, 

 and a pure strain has since been derived from it. It is to this strain 

 that later the name of scindens was given. 



According to Renner (1), the barren seeds of our plants contain 

 small fertilized germs. The failure of their development is due to 

 lethal factors, of which there are two in 0. Lamarckiana. One of 

 them is linked with the factors for narrow leaves and other char- 

 acteristics shown in the hybrids of the type velutina, and the second 

 one with the broad foliage and other peculiarities of the hybrids 

 of the stature of laeta. In 0. Lamarckiana the amphi-vi/u//na and 

 the amphi-/ae/a germs are killed by their respective lethals, and 

 only the combination of the two components produces viable seeds. 

 From these considerations it is evident that the new scindens must 

 lack one of the lethals of its parent. Furthermore, the germs of 

 velutina are usually produced in too large proportions, but those of 

 laeta in too small numbers, as compared with the figures for ordinary 

 monohybrid splitting (8). Thus the fact that only 7 per cent of 

 barren grains were counted, indicates that the seeds with germs of 

 velutina had become viable, while those with laeta germs had not 

 suffered any change in their lethal factor. In other words, 0. scin- 

 dens is distinguished from 0. Lamarckiana by the lack of the lethal 

 factor of the velutina gametes. It is probable, of course, that this 

 change was accompanied by one or more minor mutations, but these 

 must be left out of consideration in our present discussion. The race 

 must thus split off viable seedlings of velutina, besides a small 

 amount of laeta germs in the barren grains. The description of its 

 pedigree will prove the exactness of this conclusion. I propose to 



