THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 15 



the writer the best of all Oenotheras so far brought into the experi- 

 mental garden." 1 ) 



In order to determine the coefficient of mutation for 0. biennis 

 L., 1 have made a culture of about 8500 individuals, all of which 

 have been studied from their germination to the period of flowering 

 and of fruiting. In the interest of subsequent cultures they have 

 been pulled out before ripening their seeds, with the exception of 

 a sufficient number of their mutants, which were cultivated with 

 some of the true individuals in another garden. 



The seeds for this culture were taken from the pure line pedigree 

 plants of Stomps, which were derived from a single rosette of 

 radical leaves collected by him in 1905 in our sand dunes near 

 Wyk aan Zee. 2 ) In this part of our country, no other species of 

 Oenothera are growing and no intermingling of forms has to be 

 feared. From seed of this plant, self -pollinated, a second gene- 

 ration was grown in 1910 and a third generation in 1912. Self- 

 pollinated individuals of these two generations gave the seed for 

 the cultures of Stomps in 1913 and for mine in 1914. These latter 

 came from three and four parent plants, the descendants of which 

 numbered respectively 5500 and 3000. Of course I sowed almost 

 all the available seed, and their culture just covered the field at 

 my disposal outside of my experimental garden (about 600 square 

 meters). Thus all my plants belonged to the same pure line as 

 those of Stomps, and the individuals which supplied the seeds had 

 been cultivated under the most favorable conditions obtainable. 



The seeds were sown in January, the seedlings transplanted 

 into wooden boxes in March, and brought on the field in the middle 

 of April. This early sowing and transplanting is with us the most 

 effective means of making the plants annual, and in my whole 

 culture less than a dozen individuals failed to flower. 



It was possible, this time, to pick out the dwarfs from the 

 wooden boxes before the transplanting into the field. By this 

 means a second change of place was avoided, and the dwarfs could 

 be cultivated together on a bed of my experiment garden, which 

 enabled me to inspect them almost every day during their develop- 

 ment and through the whole summer. The characters which 



i) Davis, B. M., Parallel mutations in Oenothera biennis L. Amer. 

 Nat. 48:409, 19 1 4. 



2) Stomps, Th. J., Parallele Mutation en bei Oenothera biennis L. Ber. 

 Deutsch. Bot. Gesellsch. 32:179—188, 1914. 



