184 BOTANICAL GAZETTE [MARCH 
for experimental studies on mutation, the Dutch bzennis seems to 
the writer the best of all Oenotheras so far brought into the experi- 
mental garden.5 
In order to determine the coefficient of mutation for O. biennis 
L., I 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. 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 gener- 
ation was grown in 1g1o 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 
3s Davis, B. M., Parallel mutations in Oenothera biennis L. Amer. Nat. 48:499- 
IQT4. 
3% Stomps, Tu. J., ee Mutationen bei Oenothera biennis L. Ber. Deutsch. 
Bot. Gesells. 32:179-188. 1 
