1915] DE VRIES— OENOTHERA BIENNIS 189 



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 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 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 

 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 0.1-0.3 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 



