LAMARCKIANA SEMIGIGAS. 



constitution is usually either (mutant + laeta) x laeta, or (mutant + 

 velutina) x velutina. They are dominant, the mutated gametes re- 

 producing the race, whereas velutina x velutina, and laeta x laeta 

 give the barren grains. 



Among the mutants from Oe. semigigas such sesquiplex forms 

 rarely occur, or perhaps are not always easily recognized. I selected 

 two of them with 15 chromosomes, namely, ollonga and auricula 

 (de Vries 1924 b, p. 261) for self-fertilization. Moreover, two speci- 

 mens of cana with a deviating type, but with the same number of 

 chromosomes (de Vries 1924 b, p. 261) were found, after self-fertili- 

 zation, to have a uniform progeny, besides a few mutants, and 

 therefore to belong to this category. For convenience's sake I shall 

 distinguish them by the name of cana sesquiplex. They reached 

 about one-half the height of normal cana and had thicker fruits, 

 which were almost like those of Oe. Lamarckiana. The results are 

 given in table 7. 



Table 7. 

 Sesquiplex mutants of Oenothera semigigas. Second generation. 



The amount of barren grains was, for oblonga, 69 percent, for 

 auricula, 52, and for cana sesquiplex, 73 and 81 percent. Since the 

 non-mutated gametes must have been of the velutina type, which 

 is usually preferred during fertilization (de Vries 1924 a), these 

 numbers must be considered as being too high, and as pointing to 

 the expected figure of one-half of barren seeds. Setting aside these 

 and the mutants, the four lines were found to be uniform. The 

 mutants were 1 albida, 1 scintillans and 3 oblonga. 



16 -and 17-Chromosome Mutants of Oenothera semigigas. 



All of the mutants of Oe. semigigas dealt with in the above tables 

 and descriptions had 15 chromosomes in their nuclei, as far as in- 



44 



