PREFERENTIAL FERTILIZATION IN 

 OENOTHERA LAMARCKIANA. 



In the cultures of mutant races of Oenothera Lamarckiana, one of 

 the most common difficulties lies in the deviations shown by the 

 splitting phenomena from the ordinary rules. After the selffei tiliza- 

 tion of a splitting race, or after a cross, the expected types appear, 

 as a rule, but in unexpected numerical relations. According to the 

 individual cases, this may be due either to a differential growth 

 ratio of the germs within the ripening seeds, or to preferential 

 fertilization. 



The former cause prevails among crosses of the mutants 0. gigas 

 and 0. semigigas, but the second seems to be of more general occur- 

 rence. The latter may depend upon differences in individual vigoi 

 of the pollen grains as well as of the ovules. Some kinds of pollen 

 will produce tubes with a rapid growth, whereas other tubes will 

 have a slower development, as has been shown by the researches 

 of Nilsson (1) and Renner (2). Some ovules may attract the pollen 

 tubes more effectively to their micropyle than others, and this 

 supposition may explain the deviations in those cases in which 

 homogeneous pollen is used. 



We will first consider the cross between 0. Lamarckiana mut. 

 velutina (0. blandina) and 0. Lamarckiana itself, as described by 

 the writer (3). 0. blandina has only one kind of gamete, belonging 

 to the type of 0. velutina, but modified in different points, and 

 especially in having no lethal factor. The cross was made in 1913, 

 the first generation yielding as was to be expected about one-half 

 of the type 0. laeta. the other half belonging to the pattern of 0. 

 velutina. Some of the hybrids of the first group were self-fertilized. 

 After the rule for monohybrid splittings we should expect the 

 progeny to consist of 25 per cent laetax laeta, 25 per cent blandinax 

 blandina and 50 per cent laetax blandina. The first combination, 

 or 0. amphilaeta, must result in barren seeds on account of the 

 lethal factor of the 0. laeta gametes. Thus the ratio of the culture 

 resulting from the cross would become two-thirds hybrids of the 

 0. laeta type and one-third 0. blandina. Instead of this 33 per cent 

 0. laeta and 67 per cent 0. blandina were counted. 



