BRITTLE RACES OF OENOTHERA LAMARCKIANA. 



699 



give the name of 0. Lamarckiana mut. tarda to the split off velutina, 

 which constitutes a new strain. 



Table I. 

 Pedigree of Oenothera Lamarckiana mut. scindens in percentages. 



The table gives the pedigree in its most condensed form, indicating 

 the percentages as calculated for the whole harvest, and giving 

 the size of each culture. In 1917 and 1918 almost all of these plants 

 flowered and ripened their fruits, but in repeating the third genera- 

 tion in 1920, only a smaller number were planted out. Every new 

 generation was sown from seeds of a specimen of the type scindens, 

 self-fertilized in the previous one. The third generation has been 

 cultivated twice, in 1918 and 1920. The amount of barren grains 

 was determined in glass tubes at about 30° C, containing 100 seeds 

 each. 



The mutants in the second generation were lata, nanella, oblonga, 

 pallescens, and lucida-like, but in 1918 nanella, oblonga, and lucida- 

 like, and in 1920 lata, lucida-like, and oblonga. The lucida-Wke plants 

 had almost no sterile seeds (0—5 per cent) after self-fertilization; 

 they indicate the copulation of gametes, mutated into a brittle form. 

 It is evident that the mutability of 0. scindens is at least as efficient 

 as that of the parent species. The loss of the lethal factor for velutina 

 has not changed this quality. 



In 1917 I fertilized 28 specimens of the type of Lamarckiana with 

 their own pollen, and counted the barren seeds for each of them. 

 Their number varied from to 8 in 100 seeds, giving an average of 

 5 per cent, determined in a total of 2800 seeds. I also counted the 

 seedlings of the types of Lamarckiana and tarda for each of the 28 

 samples separately, and found 33—53 per cent of the first and 47—67 

 per cent of the second form, with an average of 42 per cent scindens 

 and 58 per cent tarda, as determined from about 3000 seedlings. By 



