BRITTLE RACES OF OENOTHERA LAMARCKIANA. 



703 



to yield laeta x deserens, a common hybrid which I have more than 

 once described under the name of lucida (4), and tarda x deserens. 

 This latter combination has the factor for brittleness, which is 

 recessive, on both sides, and must therefore produce brittle plants, 

 which must be expected to comply in their main feature with the 

 type of 0. velutina x deserens = 0. rubrinervis. Both the expected 

 types of hybrids occurred, as was evident from a comparison with 

 the corresponding hybrids of 0. Lamarckiana x 0. rubrinervis. 



The crosses were made in 1920, and from each of them I had 

 in the following summer a lot of 60 flowering hybrids. The brittle 

 specimens are in excess, as was to be expected. 



With 0. Lamarckiana, 0. nanella, and 0. lata, the results, of course, 

 are of a more complicated nature. I made the combinations shown 

 in table VI in the summer of 1917. 



The crosses with 0. nanella were made with pollen of two differ- 

 ent strains. The hybrids were counted in the period of well developed 

 rosettes, in which the distinguishing features were bright and clear. 

 The barren grains are given in percentages of the whole harvest. 

 The first two crosses must be expected to give the same results, 

 since both parents are isogamous. The expectation would be for 

 equal groups of laeta x laeta = barren grains, laeta x velutina = 

 Lamarckiana, tarda x laeta = scindens, and tarda x velutina = tarda. 

 The types of Lamarckiana and scindens are exactly the same, and 

 cannot be separated on the beds; the tarda appear in too large num- 

 bers, as usual. 



In the crosses between Lamarckiana and nanella, a certain number 

 of dwarfs are usually produced in the first generation, and therefore 

 might be expected here also. If we combine them with the figures 



Table VI. 

 Crosses of 0. scindens with 0. Lamarckiana, 0. nanella and 0. lata. 



