1915] DE VRIES—OENOTHERA BIENNIS.| 189 
leaves reached 15 cm. and more in length and were clearly distinct 
from the normal type of O. 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 gen- 
eration 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 O. 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 
able to carry out the experiment. It may be reduced very essen- 
tially by a previous study of the marks of the young rosettes of 
O. biennis semigigas, so as to be able to plant out almost only these, 
hoping to find the gigas among them; or by studying the external 
influences which may increase the degree of mutability of the 
parents in the desired direction. 
Sulfurea mutants have been far less rare. This was to be 
expected from the fact that Stomps had 4 of them among 920 
plants. From the parent type they differ only in the color of their 
petals, which is a very pale yellow. It is so pale that collectors, 
who see the variety in our sand dunes, often call the petals white. 
In the cultures they are easily seen as soon as the flowers open, 
especially in the evening. I found 27 of them among my 8500 
plants, making a percentage of 0.3 per cent. They occurred in 
the progeny of all the 7 parents of my stock, 13 in the third, and 
14 in the fourth generation. There were 6 parents, whose progeny 
contained o.1-0.3 per cent, and one with 0.7 per cent (of the 
fourth generation). It is possible that this last parent had been 
more favored by external conditions than the three others of the 
