THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 19 



soil, and the total height about 1.5 meters. The leaves had the 

 same form as those of biennis, but were a darker green and slightly 

 more pubescent. The pollen consisted of 3- and 4-cornered grains, 

 both of which types seemed fertile only for about a quarter. Arti- 

 ficial self-fertilization, however, had no result, and on the stigmas 

 of 0. biennis, 0. gigas and 0. Lamarckiana the effect of the pollen 

 was very slight, inducing some swelling of the ovaries but no good 

 seeds or almost none. Inversely, I have tried to fertilize the flowers 

 with the pollen of the three species named, but got a good result 

 only in the case of 0. biennis. Numerous good capsules with a 

 sufficient supply of apparently good but in reality empty seeds 

 have been obtained by leaving the flowers free to the agency of 

 insects in the midst of the thousands of their flowering sisters, 

 while in the same garden no other Oenotheras were grown. 



The three vigorous specimens of the mutant produced some 

 lateral rosettes at the base of their stem, even as we have seen in 

 the case of the parent species and the dwarf variety. These rosettes 

 were isolated and planted in pots in the beginning of August; 

 four of them were very vigorous, but the other one rather weak. 

 They have thrown off lateral rosettes themselves, and the stems 

 repeated the production in two instances. It is proposed to try 

 to bring these plants through the winter and repeat with them 

 the culture and the experiments of this year. After a month their 

 leaves reached 15 cm. and more in length and were clearly distinct 

 from the normal type of 0. biennis, being much broader and a 

 darker green. 



Of the four semigigas mutants, two arose from the seeds of the 

 same parent which yielded the semigigas of Stomps in 1913. All 

 three belonged to the third generation of the pedigree. The two 

 others were derived from two different parents of this same 

 generation and therefore belonged to the fourth. The reason why 

 three of the five came from the same lot of seed was probably no 

 other than that the harvest of this plant had been the largest. 

 More than one-third of my whole culture (3200 plants) were children 

 of this mother. 



No gigas with 28 chromosomes and fertile pollen occurred in 

 my culture. With a chance of one sexual cell mutated into 0. gigas 

 in every 2000, the expectation for the copulation of two such cells 

 is evidently only one in every 4,000,000. This would require a 

 garden of more than five or six acres (two hectares) and the corre- 

 sponding cost of labor. Perhaps some American institution is 



