BRITTLE RACES OF OENOTHERA LAMARCKIANA. 707 



0. tarda x deserens and its reciprocal also reproduced the two 

 types of 0. tarda, among 53 and 60 flowering specimens giving 50- 

 60 per cent tarda and 40—50 per cent pallida. 0. deserens has the 

 same stature and brittleness as 0. tarda, but no lethal. 



0. tarda x 0. Lamarckiana and its reciprocal cross yielded plants 

 of the types of both parents, in cultures of 54 and 52 flowering 

 plants giving 40—60 per cent tarda and 60—40 per cent of the La- 

 marckiana type. The calculation for this cross is tarda x laeta, 

 tarda x velutina, pallida x laeta, and pallida x velutina. The first 

 combination must give barren grains, the second must give the type 

 of tarda, the third that of Lamarckiana, and the fourth combination 

 evidently results in specimens of the type of tarda, since no plants 

 like pallida were found. Thus we see that the different crosses prove 

 the formula for 0. tarda = tarda x pallida, as already given. 



Conclusion. 



The genetical constitution of the three races may be expressed as 

 follows: scindens = laeta + tarda; tarda = tarda + pallida; and pal- 

 lida = pallida. 



The factors involved in the origin of these races are (1) for laeta 

 the same as in 0. Lamarckiana; (2) for tarda the same as in the 

 velutina gametes of 0. Lamarckiana, with the factor for brittleness, 

 but with the lethal factor of the laeta and without the lethal factor of 

 the velutina; (3) for pallida the same as in tarda, but without lethal 

 factors, and with a factor for broader foliage and one for paleness 

 (small amount of red color). The two latter factors may have been 

 derived from the laeta gametes. 



Pallida is a homogeneous race, like deserens, blandina, and deci- 

 piens. Of these, deserens is also brittle, but in blandina and in deci- 

 piens this character is absent. 



LITERATURE CITED. 



1. Renner, O., Die tauben Samen der Oenotheren. Ber. Deutsch. Bot. Gesells. 



34 : 858-869. 1916. 



2. Uphof, J. C. T., An historic spot for students of genetics. Jour. Heredity 



13 : 343-345. 1922. 



3. Vries, Hugo de, Gruppenweise Artbildung. Berlin. 1913. 



4. , Oenothera rubrinervis, a half mutant. Bot. Gaz. 67 : 1 — 26. 1919, 



Opera VII, p. 353. 

 5. , Oenothera Lamarckiana erythrina, eine neue Halbmutante. Zeitschr. 



Ind. Abst. 21 : 91-118. 1919, Opera VII, p. 386. 



